For the case of TB vs RTwP , I personally think both were great combat mechanics, but Larian has huge experience for Turn Based combat and I think they should keep at it. Some suggest why not try TB and RTwP both. Yes it may be possible but it will be time consuming. I suggest the game should be released with Turn based combat mechanics. Later the RTwP mode can be added for satisfying the die hard RTwP fans.
They've made action RPGs too. What's the rush? Economic forecasts aren't very peachy right now.