Fallout according to the history I've read WAS REALTIME, at first...
(Talking about GURPS Proto-Fallout here... supposedly the OLD fallout demo has some of this...should take a look someday)
Clearly the combat did not work out as intended, thus fallout was made TB
Its just possible that Fallout 3 will be Turn-Based. Yes, the logic here is that Final Fantasy 1,2,3,4,5,6,7,8,9,(whatever the current # is) being mostly TB combat (actually I have no idea past 8...) have sold bucket loads worth of games.
Therefore the marketing Droids know that JRPG style TB combat will sell.
Thus a TB Fallout 3, even as a console game will do well.
However I suspect if we get TB combat, it will be at the loss of something else, say an open world? multiple paths thru quests...who knows.