DISCLAIMER: I don't know anybody, and nobody I know knows anything. This is based on no inside information at all, just on "the shape of the river."
Fact 1. G5 schools are running steady $10-20M athletic deficits, including Rice.
Fact 2. Non-FBS schools are running $10-$15M athletic deficits.
These two, in conjunction, generally mean that dropping from FBS is a bad idea.
Fact 3. Rice's stadium is over 50 years old, and new stadiums are expensive.
Conjecture: With the escalating cost of competing in FBS, that $10-20 number becomes $15-25.
Fact 4. Looking at an athletic conference as a group of peers, Rice has shifted from having peer-competitors SMU, Tulane and Tulsa to a conference completely composed of large, public, academically weak schools (compared to Rice). I could be wrong, but I don't think anyone in C-USA 2015 is in the US News Top 200 National Universities.
Fact 5. Rice had McKinsey consulting look at their Division options in 2004. McKinsey recommended Division III, before an alumni and booster backlash changed the Board of Trustee's minds.
OP's Note: This "fact" turns out to be FALSE. To the extent that McKinsey made a recommendation, it was Division I-A, with Division III as a possible but inferior option, and all other options (I-AA, DI-NoFB, II, NAIA) as horriblenogoodterribadno.) My information came from this link: http://www.ricefootball.net/04athleticsbrouhaha.htm to articles by Rice boosters/alums/fans. I have since read the McKinsey report.
I apologize to Rice for any damage to Rice's athletic reputation, and apologize again for anyone whose belongings I may have been sick on at Prospective Student Weekend Fall 1990, which due to a huge oversight was also Homecoming Weekend.
I am told I had a great time, although I remembered very little, beyond being left at the football game to sober up.
Fact 5a. Those boosters and alumni, and Rice's SWC glory days, are 10 years older.
Fact 6. Rice would be a good fit, profile-wise, with the Division III UAA--Chicago, Brandeis, NYU, Carnegie-Mellon, Washington U in St. Louis.
http://www.uaa.rochester.edu/
I wonder if the answer to C-USA being at 13 is Rice folding.
OP Note: No.