S&Box has been discussed a lot but the game is completely different to GMod to the point where everything would need designing and rebuilding from the ground up, and with everything up in the air about how addons and the sandbox mode is going to work I don't think it's going to happen.

The focus is to get this addon for GMod in a really good state and just have that be the TARDIS you can play with, abandoning GMod this late into development to redo everything in sbox is really just not worth it. Maybe it will happen one day, but it's unlikely to be done by the current team if it does.

Alright ! That answers my question. Thank you very much ! Very great addon btw.