Board Game Arena

For the moment the replay system is very limited.
An addition that would make it more usuable would be to be able to
go back and forth a move on the replay but I understand their might be technical issues.
A most advanced feature would be to be able to explore alternatives but probably too much

Yes. This.

Currently, going back requires going to the beginning of the game.
(at least as far as I'm aware)

Unfortunately, from my understanding, most of the games aren’t programmed such that you can go backwards. Each step in a game isn’t saving the entire game state but just the incremental step and programming for a game would only allow you to go forward. This is also why you can’t just load up a game state in the middle, it has to start at the beginning and step through all the moves to get to a spot in the middle of the game.