[nfhammes]

Number of teams on an alliance: 2v2? like FTC and old FRC? Could be interesting.
Number of alliances in a match: Unless they make it 2x2x2x2, would probably make modifying the field really expensive.
Match length: They can change it a bit, but there's event scheduling issues.
Bumper rules: These have changed frequently. Not that exciting.
Field surfaces: Low-friction surface, anyone?
Robot size: I don't see this changing too drastically either.