I don't think so. TCP API is unchanged. Older clients can still connect using JSON encoding, so you should be fine. The client needs to explicitely "ask" for msgpack encoding and the web app will do it.

I've tried to test everything as much as I could and I think it will work just GREAT :-)

Now, regarding the bet pruning - I got a lot of feedback and most people told us that keeping historical bets is NOT that important. Besides, most sites keep deleting old data anyway. I'll give the idea a few days, maybe I'll find a nice (technical) solution to keep old bets somewhere and keep them accessible, while having the recent data ultra-fast.

Thanks and cheers!
Ethan