A321N can operate OTP-CMB routes without a problem, same goes with CMB-MXP, CMB-FCO and maybe even CMB-ZRH? etc.. UL could pick up A321NX/NYs to begin routes to those destinations, UL could also use the A321 XLR or LR or NEO for that matter on long haul routes where much demand is not needed for a widebody aircraft, such as PVG-CMB, PEK-CMB, ICN-CMB etc.

A321Ns can be used as a replacement for A320's that UL has..

To run above routes efficiently, UL should have at least 35 aircrafts and at least 15 of them has to be long range widebodies.

UL may keep around some 320s considering they do certain routes such as GAN.
considering that the A321N is more fuel efficient than the A332, I guess it would be viable to go that way,(correct if i'm wrong)
as of A321NX, which would be better- the -251NX, the -252NX or -271NX or the -272NX

also, any updates on the following?
AND
ANE
ANF
ALH
ALM
ALN

Doesn't know about ALM, ALN is on weekly maintenance, as I heard, one A21N is near the hangar, one was at Apron Echo.

A321-27#N# is bit dangerous, Better to go with CFMI Leap 1A engine option, and also Better to consider LR version and also Business class configuration with 1-1 full lie flat seats just like Iberia's A321XLR cabins or Air Astana's A321N cabins. It will help UL to maintain long haul routes even in off-seasons instead of A332s, and also to cater short-haul routes instead of using dated A320ceos..

you're absolutely correct about the problems around the GTF(271/272) since it's still a relatively new design
but then, I also heard of problems around the LEAP as well, specifically in IndiGo's A321Ns.
A321 is the closest you might get to a B757(which is a medium-long haul narrowbody), and I see airlines like EXS replace their 757s with 321NXs
considering that the XLR started delivering in Oct 30th and having a significant backlog, UL might not be able to get their hands on one in the near future, rather by 2030 or later.
or they could go by dry-leasing A321N/LRs from other airlines(if that's economically correct to do and if airlines agree to lease them)
(I still have some questions about A321s serving lower passenger demand routes instead of A320s, or did you mean UL retiring the 320CEO and retain the 320NEO?)