Many months ago we saw work in progress shots of the new P-51D exterior model, and features like the landing gear were being reworked in extremely high detail. That being the case, I think the new AccuSim P-51D will be released just like the Wings of Power 3 Thunderbolt -- a completely new model to buy plus the AccuSim pack as an optional expansion.
I'll strengthen my argument by pointing out that the WoP2/Solo Mustang is really an FS9 legacy model that was updated to be used in FSX, and a true FSX version is overdue. (Remember that the WoP2 Thunderbolt had just been upgraded for FSX shortly before the WoP3 version came out.) Conversely, the WoP2 B-17G was built as an FSX model and that allowed for an AccuSim 'bolt on' expansion.
_________________I like Thunderbolts!
(Link to MySpace tribute page)120th Fighter Wing, Montana Air National Guard