Sounds like a really interesting design.
Only So far i found 3 possible weak points, but i guess you know them and either it's worth to have them (most likely) or you didn't find a way to build around them. Well, at least i have questions about why you build it that way^^

1. Motor inside the wheel:
Sure saves a lot of space (and some weight) but from what i have seen the wheels are amongst the most often damaged parts.
Putting something as valuable (well, depends on the motor, but i count all the machining need in here) to a place that likely to get hit sounds like a risky option. Might be worth it, if you can machine it yourself, and the motors aren't too expensive/if you are willing and able to have enough spares around.

2. Springs tend to loose a bit when keeping them under pressure.
Heavily depends on the kind of spring you use, and i doubt the effect would be noticeable in our short "active" periods. Just maybe something to keep in mind.

3. Springs for the actual flip, and pneumatics to compress them again. Interesting Idea to design it that way round, but you'll need a lot of air to get those compressed (but you can do it a bit slower than the air is used normally, so less valve freezing).
Possible problem i see here: if anything in your pneumatics get damaged, you'll stay there with the flipper wide open, possibly showing all your inside vulnerable. Others might still work as wedge without their pneumatics, you won't.