Board Game Arena

Curious if anyone is using, or know of BGA's platform being used for prototyping purposes. I'm working on a board game and am at the stage where I'd like to begin prototyping. I can do so on physical paper obviously but my own play group is small compared to the people who'd help if we could play online.

This would therefore be a game quite a long time away from being published, not sure if that's something BGA allows or if they only want published games they can add to their games list.

Unless there is no way to represent your game with cardboard and counters, that is the appropriate way to prototype a board game. It will be lots faster and easier.
There could be minor exceptions - for example if you were only investigating tweaking a rule, and had access to a complete implementation you could modify.
Even if you were forced to use a computer to develop a game that might be implemented on BGA eventually, I'd start with a generic visual-only engine like vassal.
..and of course, if you're a programmer and just want to write some code, go ahead - it doesn't have to make sense to anyone but you if it's fun.