-- Shoreliner I's date to 1982 and got 2 sets of midlife rebuilds: '96 and '08. Too shot for rebuild #3, and a small fleet at 43. They're toast, both the red ones and blue ones.
-- Shoreliner II's built '87-88, rebuilt '08 simultaneous with the Shoreliner I's. Also a small fleet at 29. Not economical to rebuild, so those probably go simultaneous with the I's.
-- Shoreliner III's and IV's are near-identical, built in multiple installments '96-02. Never rebuilt. 106 III's, 10 active IV's + 1 IV wreck victim that's probably never coming back.
-- East-of-Hudson Comet II's were built '82, rebuilt '99 and '09. 29 active. Toast, and NJT is purging all its Comet IIM's as first order of business so no upside in keeping the oldest ones fresh.
-- West-of-Hudson Comet V's were built 2004. 64 active.
Of these, CDOT owns 23 of the I's, 10 of the II's, and all of the IV's. The Shoreliner III's and Comet II's are MTA-only. Comet V's are west-of-Hudson -only.
The MTA intends on going all bi-level. They have no choice EoH with Upper Hudson and Upper Harlem capacity problems, so that's a complete purge of the Comet II's and all the blue Shoreliners of every class. Comet V's are intertwined with NJT's purging strategy which targets 2025 as the year they achieve 100% bi-level. NJT has 260 Comet IIM's and IV's it has to dispose of first before it even gets around to a decision on option orders for replacing the V's, so another 10 years of service on the WoH fleet before replacement is a pretty solid bet.
For CDOT it depends. They can join in on the MLV order...but play red tape with with the MTA on which ones get assigned to the MNRR branchline pool vs. the CDOT-solo pool. Or they can play scrap-n'-swap by junking all their Shoreliner I's and II's, and swapping title deeds with the MTA on a selection of III's to send out for rebuild. Maybe even junk the Mafersas in the process and take on more ex-MTA III's, because then they'd have a uniform-lineage Shoreliner III+IV fleet that can all go into GCT (Mafersas can't because of underclearance issues). Rebuilding flats isn't economical for all that many agencies nowadays, but CDOT could probably justify it if it went all-in on a decision for uniform rehabbed fleet with padded numbers that cover all foreseeable service expansion during their rebuild lifetime. Say they pick up 80 of the 106 III's from the MTA to replace 33 I's and II's, 33 Mafersas, and 1 wrecked IV...and add 13 units of expansion to cover Waterbury/Danbury headway improvements, Hartford Line full-blast service, and future-proofing for some combination of New Milford extension / Hartford-Waterbury / joint MassDOT run-thrus from Northampton/Greenfield to Hartford. Then cannibalize or store the remaining 26 units as parts cache for the rebuild program to bring down the total cost of the program. Unless the MTA wants to hold on to a few sets for work trains, excursions, or something.
^That^ they can probably get good value out of if they aren't up for buying all-new or fighting it out with the MTA for what can get assigned outside of MNRR ops.