Hello :)
I still visit but I'm yet to find a way to add new bricks, though it might be possible by messing with the internal files once I work out how to build the correct brick files... then again it might, at best, be only a limited number by swapping out other bricks that are dupes (due to some bricks having multiple IDs) or little used *shrug*.
In the mean time I am still adding sets to my github:
https://github.com/PhoenixRiver/bricksperience-models
which you can add to Bricksperience (BS) by putting the"sav" in your user account's AppData/Local/TheBricksperience/Saved/SaveGames directory or importing the "ldr" files into the editor and setting them up with the build order and other stuff (it's why I supply the binary BS files... the big sets are a lot of work indeed!
P.S. Tell me if you finish the London Bridge model but I'll warn you, it is over four thousand pieces and gives even beefy computers a run for their money until you've built a lot of the pieces... too many pieces to calculate physics for!