There are plenty of places that TW could go that it hasn't yet.

My fear is that they keep releasing horribly buggy versions with poor design decisions (star forts...) & sales keep dropping until they just stop with no competitors.

It'd be not so bad if someone released a decent quality competitor series about the same time.
But there is a good reason that nobody really has come anywhere near to making a competitor to the TW series: Its an astoundingly massive & complex undertaking.