Would the NFL every seriously consider divisions with only three teams? In some ways this might be a more attractive option than divisions with six teams.

This could possibly come about if the NFL decides to expand to Europe. Adding four teams would require either divisions of inconsistent size (4 or 5 teams) or US and European teams sharing a division. Adding only three European teams would allow them to be all in the same division, and still allow the NFL one expansion team in North America.

AFC
Europe - London*, Frankfurt*, Munich*
East - NY Jets, New England, Buffalo
Central - Kansas City, Indianapolis, Houston
West - LA Chargers, Las Vegas, Denver
North - Baltimore, Pittsburgh, Cleveland
South - Jacksonville, Miami, Tennessee

NFC
Atlantic - NY Giants, Philadelphia, Washington
North - Detroit, Chicago, Cincinnati
Southwest - Dallas, Arizona, New Orleans
Pacific - Seattle, San Francisco, LA Rams
Central - Saint Louis*, Minnesota, Green Bay
Southeast - Tampa Bay, Atlanta, Carolina

For a 17 game schedule:
4 games in the division
10 games in the conference outside your division
3 games against one entire division in the opposite conference

The non-division games in your own conference would be based on the previous season's standings. For example, if Dallas was first in the NFC Southwest, they would play the teams that finished second and third in each of the other divisions the year before; for the NFC Atlantic this would be New York and Washington, for the Pacific this would be Los Angeles and Seattle. They would not play the other teams that finished first in their division the previous season.

For an 18 game schedule:
4 games in the division
3 games against one other division in your conference (rotates on 5-year cycle)
5 games in the conference outside your division based on previous season record
6 games against two entire divisions in the opposite conference

This schedule would actually create a situation where teams not in the same division could actually play each other twice during the regular season, but it would only be for one opponent.

The NFL could learn a thing or two from what college football is doing. The NFL should get rid of divisions and go to flex protect conference schedules.

So the NFL should go with 2 18-team conferences, with no divisions, where each NFL team can have 0 to 2 teams that they play home and home every year. They play a total of 17 games a year. 12 games against their own conference and 5 against the other conference.

East conference (designated rivals)
1. Hamburg* (Lon, Frank)
2. Frankfurt* (Lon, Ham)
3. London* (Ham, Frank)

4. NE (Buf, NYJ)
5. Buf (NE, NYJ)
6. NYJ (NE, Buf)

7. NYG (Philly, Wash)
8. Philly (NYG, Wash)
9. Wash (NYG, Philly)

10. Car (Atl, Tenn)
11. Atl (Car, Tenn)
12. Tenn (Car, Atl)

13. Jax (Mia, Tam)
14. Mia (Jax, Tam)
15. Tam (Jax, Mia)

16. Balt (Pitt, Cle)
17. Pitt (Cle, Balt)
18. Cle (Pitt, Balt)

West conference
1. Mexico City* (LV, LAC)
2. LV (MC, LAC)
3. LAC (MC, LV)

4. LAR (SF, Ariz)
5. SF (LAR, Ariz)
6. Ariz (LAR, SF)

7. Sea. (Den, KC)
8. Den (Sea, KC)
9. KC (Sea, Den)

10. Minn (GB, Chi)
11. GB (Minn, Chi)
12. Chi (Minn, GB)

13. Det (Indy, Cincy)
14. Indy (Det, Cincy)
15. Cincy (Det, Indy)

16. Dal (Hou, No)
17. Hou (Dal, NO)
18. NO (Dal, Hou)

I'm not sold on the non-U.S. markets ever becoming more than fun talking points. Presuming no one relocates and the NFL gets to 36 with just U.S. markets: Portland, San Antonio, San Diego, and St. Louis. Also presuming the AFC/NFC remains intact with no teams switching conferences: San Antonio and San Diego to AFC; Portland and St. Louis to NFC.

I like the scheduling ease of triplets but I really think a 2x3x6 model will be the future.

AFC
Central: Cincinnati Bengals, Cleveland Browns, Houston Texans, Indianapolis Colts, Pittsburgh Steelers, Tennessee Titans
East: Baltimore Ravens, Buffalo Bills, Jacksonville Jaguars, Miami Dolphins, New England Patriots, New York Jets
West: Denver Broncos, Kansas City Chiefs, Las Vegas Raiders, Los Angeles Chargers, San Antonio Slingers, San Diego Breakers

NFC
Central: Carolina Panthers, Chicago Bears, Detroit Lions, Green Bay Packers, Minnesota Vikings, Tampa Bay Buccaneers
East: Atlanta Falcons, Dallas Cowboys, New Orleans Saints, New York Giants, Philadelphia Eagles, Washington Commanders
West: Arizona Cardinals, Los Angeles Rams, Portland Jacks, San Francisco 49ers, Seattle Seahawks, St. Louis Flyers

But if I made the conferences geographic:

Eastern Conference
Atlantic: Baltimore Ravens, Buffalo Bills, Cincinnati Bengals, Cleveland Browns, New York Jets, Pittsburgh Steelers
Metropolitan: Carolina Panthers, Dallas Cowboys, New England Patriots, New York Giants, Philadelphia Eagles, Washington Commanders
Southeast: Atlanta Falcons, Jacksonville Jaguars, Miami Dolphins, New Orleans Saints, Tampa Bay Buccaneers, Tennessee Titans

Western Conference
Midwest: Chicago Bears, Detroit Lions, Green Bay Packers, Indianapolis Colts, Minnesota Vikings, St. Louis Flyers
Pacific: Los Angeles Chargers, Los Angeles Rams, Portland Jacks, San Diego Breakers, San Francisco 49ers, Seattle Seahawks
Southwest: Arizona Cardinals, Denver Broncos, Houston Texans, Kansas City Chiefs, Las Vegas Raiders, San Antonio Slingers

Or if I did a 4x9:

Eastern Conference
Baltimore Ravens, Buffalo Bills, Dallas Cowboys, New England Patriots, New York Giants, New York Jets, Philadelphia Eagles, Pittsburgh Steelers, Washington Commanders 

Northern Conference
Chicago Bears, Cincinnati Bengals, Cleveland Browns, Detroit Lions, Green Bay Packers, Indianapolis Colts, Kansas City Chiefs, Minnesota Vikings, St. Louis Flyers

Southern Conference
Atlanta Falcons, Carolina Panthers, Houston Texans, Jacksonville Jaguars, Miami Dolphins, New Orleans Saints, San Antonio Spurs, Tampa Bay Buccaneers, Tennessee Titans

Western Conference
Arizona Cardinals, Denver Broncos, Las Vegas Raiders, Los Angeles Chargers, Los Angeles Rams, Portland Jacks, San Diego Breakers, San Francisco 49ers, Seattle Seahawks

Thinking about if NFL had 3-team divisions in 1971

1971-1975
AFC east: Buf, NYJ, NE, Balt
AFC north: Cle, Cincy, Pitt
AFC south: Miami, Hou, KC
AFC West: SD, Oak, Den
NFC East: NYG, Philly, Wash
NFC North: GB, Minn, Chi, Det
NFC South: Atl, St Lou, Dal
NFC west: LA, SF, NO

1976: add Tam to AFC South
1976: Move KC to AFC West
1976: add Sea to NFC West
1976: Move NO to NFC South
1981: Raiders move to LA.
1983: Colts moves to Indy
1988: cardinals to Phx
1988: move Cards to NFC West
1996: Jax jags to AFC South
1996: Car to NFC East
1996: Rams to St Lou
1996: Browns to Balt
1998: Oilers to Tenn
1999: expansion in Cleve. AFC North
2002: expansion in Hou NFC South

And to build on that, the NFL could have gone to 5x3 in each conference in 1996:

AFC
West - SEA, Raiders, SD
North - BAL, CIN, PIT
Central - KC, DEN, Oilers
South - MIA, JAX, IND
East - Jets, BUF, NE

NFC
West - SF, AZ, Rams
North - GB, CHI, DET
Central - DAL, NO, MN
South - ATL, CAR, TB
East - Giants, PHL, WSH

I still think Browns 2.0 and the Texans both wind up in the AFC (having the Texas teams on separate conferences worked for how the TV contracts were structured at the time), and Seattle still moves to the NFC in 1999. Denver moves to the AFC West, the Colts move to the Central, the Tennessee Oilers/Titans join the South, and the Texans join the Central. Seattle joins the NFC West, the Saint Louis Rams join the Central, and Minnesota moves to the North for the NFC's sole four-team division.