I'm confused--you're not saying the T wants to truncate service on the Providence CR line by dropping Wickford Junction as a stop and bring the new terminus up north to TF Green*? Sorry if I'm taking you too literally--surely you mean something else but that's how it reads (to me).
(*Or, the artist formerly known as TF Green now known as Rhode Island International Airport (at one point? except I haven't seen any major signage changes) except the abbreviation is PVD implying it should be called Providence Airport but why don't we just say screw it and rename it Vincent Cianci Airport to cash-in on the biggest branding opportunity still going in lil' ole RI & the Providence Plantations...)
Wickford is RIDOT's baby, and they envision it as a linchpin of their various intrastate service patterns once the whole shebang is built out. As it precedes the 'pure' intrastate service that never crosses the MA border, the only schedule you can hang on it right now are these infrequent Providence Line super-extendeds that are too long on-the-clock to run in any quantity. The station itself is also only half-complete and has limited capacity for service; both it and T.F. Green it will eventually get new northbound platforms added to transform them into quad-track stations with 2 side platforms and 2 center Amtrak expresses. There's more track work to do like raising the speed limits on the turnouts the T uses. And RIDOT is set to construct a mid-line layover yard and small maintenance shop at West Davisville to de-clog crowded and rapidly approaching-capacity Pawtucket layover, cut down on the cost-chewing non-revenue miles it currently takes to deadhead an out-of-service train to/from Wickford, and re-prioritize Pawtucket for the Providence Line.
The only reason the T is being dragged into serving these far-flung stops--which may also include rebuilt Kingston before too long--is that they are bound by the Pilgrim Agreement MA signed with RI for out-of-district commuter service. In that agreement (which has been amended a few times now) RI contributes a % ownership stake to the commuter rail fleet--all of it, northside and southside--that auto-scales to service levels, running miles, and duty cycles spent across the border. They also reimburse costs, square staff arrangements for RI-based Keolis staff, adopt all of the T's RR design and accessibility guidelines, coordinate capital spending, allow RIPTA buses to cross the border to South Attleboro, and square all revenue sharing. In return, the T is required to be RIDOT's mercenary operator for all intrastate commuter service, including the to-be services that never touch MA soil like Pawtucket-Westerly, Woonsocket-Wickford, or this Urban Rail service spanning Providence Metro from a few posts up. Those trains will fly under the T logo even though they're out-of-district, because RIDOT's subsidy has already auto-scaled to pay for the equipment.
So...the Pilgrim Agreement is a pretty sprawling and complicated document. But it's also very
elastic to future needs because RIDOT doesn't have to beg for the T's mercy to initiate new service; their subsidy snaps up another rung. The T likewise makes pretty good money on the deal taking cash to do someone else's bidding guilt-free (and very often with fewer headaches than dealing with in-district constituencies), netting more buying power with each new fleet procurement because the RIDOT ownership shares keep increasing, and netting a bigger footprint for major initiatives like RER and electrics that would be driven top-down by Providence Line growth. It's also an agreement that MA taxpayers should be happy about, because it's making the agency beneficial revenue.
Overall, the T is very happy with this arrangement. And they'll make more money still when they're running the 'pure' intrastate service. But right now an incomplete Wickford is an awfully long schedule to pick up awfully few people. And it's a strain on limited South Station capacity because of how extremely far it has to go to time itself against terminal district congestion. It is a bona fide ops pain to take a standard Providence Line schedule out that far vs. maybe being able to reset the schedule to cram in another 1 or 2 max-revenue Providence turns. MassDOT had hoped by this point that RI would've been able to stimulate some/any non-embarrassing ridership there to show some results, and show that they could start accelerating their intrastate buildout a little faster. Because the faster it gets built out the sooner the 'pure' intrastate trains can pick up that stop and the T can start pulling back to "right-size" the standard Providence Line schedule at a maximally efficient length and time. Something that they'll have more pressure to do with the new Pawtucket stop being an add to all schedules (and close enough to the border to be a South Attleboro load relief conern), and something they'll definitely need to do for RER which isn't going to play so well with extreme-outlier schedules.
Wickford doesn't project useless over the long-term--it's too early, and the real payoff was always considered very long-term--, but there's no doubt it's underperformed initial expectations by a concerning margin. Nothing in the demographics has shown there's much of a latent Boston commuter audience here that would be taking the cheaper/slower commuter train vs. grabbing a Northeast Regional at Kingston. It's a lot of Providence Metro exploits and converging paths from RIPTA buses. So with the growth small and the ops messy the T is going to want its Providence Line schedule back, truncated at the optimal distance for packing it full of more slots.
Where T.F. Green comes into play is that Amtrak has shown interest in a platform on the middle two tracks for sending some NE Regionals there...something it would have bandwidth for doing since a ConnDOT Shore Line East extension to Mystic and Westerly would allow them to drop those two minor stops completely from the Regional schedule and roll up at Green. That, along with it being a decently-established regional airport with upside, makes a little dilemma about whether to dig in the regular Providence Line schedule at Providence or Green once the intrastate service has taken over Wickford. Also complicating that choice is that Cranston will be an infill between Providence and T.F. Green by this point, and the Olneyville infill that was rejected (uncertainty over 6-10 Connector construction) may be a high-priority re-add. Do those get added to a Providence Line schedule that's terminating @ Green, or are they only handled by the intrastate trains.
Clearly a lot to hash out there. What's fairly certain, though, is that Wickford itself projects too much a square-peg for too much of the foreseeable future on Boston commutes for all that extra running distance to be allowed to chew up the schedule margin. So somewhere in the future when the intrastate service has reached some mutually agreeable stability the Providence Line will need to pull some retreat somewhere closer to Providence.