It's running on the same engine, I doubt that it's a big investment to make it modable and general trend is "modable is free content" and Larian have been very consumer friendly so far.
The same-"ish". It'll have been significantly updated by the time BG3 is ready for release and I dare say file formats and what-not may change, much the same as with Morrowind to Oblivion to Skyrim. Though the basics were the same, each one still required new tools to be made available so I'm not expecting to have e.g. a GR2 converter available from the outset, unless there's a specific effort to include one.
