Based on what they announced so far, these would seem to be the next logical adds from existing city pairs. I guess next set of route additions would be for where demand would like to emerge in second half of 2021.
EWR-BNA/MSY/ORD/DEN
LAX-GUA/PHX
AUS-LAS
SFO-LAS/SJD
RDU-LGA/SAN
New cities would probably be of the leisure category. So I'm guessing SAL and PTY.
JFK/LAX/FLL-SAL
JFK/LAX-PTY
Domestically, not too many leisure spots left, so I'm guessing IND
JFK/BOS/EWR/FLL-IND