Off the top of my head where mainline has returned to (not necessarily completely replacing Express) over the last couple of years.

MSN
ORF
STL
IND
EUG
BTV
JAX
CHS
PWM
FSD
MKE
CVG

I'm sure there are others.

And as the 777A models get converted to a high density domestic config for hub to hub and Hawaii flying, that frees up narrowbodies to go to the spokes. In addition the 65 737-700's and 21 (TK number from my PC last week) used 319's coming will accelerate the change in domestic flying.