...We might also figure in that the Khitomer truce would give Starfleet the opportunity to stop doing stopgap purchases and life-extending refits and other such nonsense, and simply start mass-producing all-new, superior ships.
This because a) there would be funds freed when there was no (or reduced) need to stay on constant guard against the Klingons, and b) it would be acceptable to have a short, deep dip in Starfleet strength, due to the complete remaking of the fleet, as long as the Klingons were down for the count.
Starfleet couldn't know how long the truce would last. But for a few years at least, they could reasonably well trust that the only maneuver the weakened Klingons were capable of would be a desperate suicide sally to save the Empire - and that the events of ST6 had made that sort of an attempt very unlikely.
So, bye bye, Constellation
class and other attempts at getting at least some mileage out of the LN-64 engines and other such outdated technology (Rick S did say that only a handful of those weird contraptions were built). Bye bye, old Constitutions
. Bye bye, experiments at renovating or reinventing the Constitutions
. Welcome, all sorts of new ideas - but while those are being tested, welcome, standardization on a limited number of the most modern designs in service.