We actually implemented live PvP in Puzzle Quest, Galactrix, & Puzzle Quest 2…
The main design issue (one of turn timing) was an issue in those games too, but we solved it with a short-ish turn-timer (it could be adjusted from 4 sec to 24sec in PQ1 for example). We also stamped out endless looping by putting cooldown timers on individual spells. So the design issues are all addressable, I believe.
The main issue with Gems of War is the server infrastructure. Due to the rather flaky nature of many mobile connections & the need to stop blatant hacking, we’d need to move a lot of the game-state simulation from the clients to the server. That’s quite a hefty task, not just in the amount of server coding required, but in the amount of rewriting of the client-server interaction.
All that being said, we’d LOVE to do it one day - it would certainly provide a challenge - but we won’t be in a place to start this in the next 6 months, I don’t believe.