Fairly certain the most successful RPG in recent years with tactical combat is DA: I, which is RTwP,
Pity successful doesn't mean "good". DA: I was a yawn fest as far as combat was concerned for me. Easily the worst of the series. The damn thing nearly plays itself at times. It certainly shouldn't be any model for a prospective BG3 to follow, successful or otherwise.
I'll also have to gently disagree with you regarding the system for a potential BG3. Whilst it makes perfect sense to follow tradition of real time with pause and I'd have no problem if they went in this direction, my counter argument is that it's even more logical to go back further to the roots of AD&D. We haven't had a quality AD&D product for years and for me, hearkening back to the Goldbox games by incorporating a deep AD&D turn based system would be a wonderful way to go. Give us a full complement of six characters though; none of this half assed 4 or 5 character nonsense.
I did think this was going to be D:OS3 at first to be honest, although that assumption is probably too obvious as others have stated. The diablo-style III is worrying though and I really wish they wouldn't choose to do this, but rather simply make another AD&D game in the Forgotten Realms. There's been too many failures by modern developers at making genuine sequels recently for my taste. (Bard's Tale IV and Underworld Ascendant) and it'll take me awhile before I'm confident in gathering my party and setting forth on this one.