I've not forgotten about Steam P2P as it's a huge opportunity to create not only a very smooth gameplay experience as a possibility to join people that otherwise couldn't play together.
Currently I've taken a step back from it all and I'm trying to engineer a way of it working the best. What I mean by this is that, by the end of the implementation of Steam P2P System, the game will be very different gameplay wise.
I'll give more details soon but for now here's what I'm thinking it will be the steps to play online when the system is done:
[Create/Join Steam Matchmaking Lobby] => [Lobby Owner chooses map] => [Every Player sets as Ready] => [Lobby Owner Starts the game] => [Every player reports his actions to everyone (p2p)] => [Actions applied in other clients and physics are locally simualted] => [Once the player ball stops, physics are re-checked and errors are fixed]
This is just an outline of how the system will play out.
Regarding the so called "gameplay differences", I'll add in-game text chat too thanks to this wonderful steam service.
This should be done in the next (hopefully few) weeks and I hope that it really works in practice as good as it works in theory.
Thank you for your support and happy playing!