Too complicated. What I think you'll eventually see is CCCR get roped in.
1. Cape officials are searching for property to publicly acquire on the other side of the bridge for an infill station (or at least to hold in-pocket for when enough additional speed upgrades are complete to allow for more scheduled infills). First attempt last year was behind
Gallo Arena about a half-mile from Bourne Rotary, and it didn't take because the trackside access was poor. Next site they're sure to look at is the
DPW lot underneath the Sagamore Bridge, which has excellent road access from Exit 1C.
2. We already know from discussion on the previous couple pages and the separate topic on NE Railfan that there is an unfunded MassDOT CIP line item for a Cape Jct. wye that would allow CCCR to move between Cape Main and Falmouth Branch without inducing a bridge opening and backup move. This line item appears to be directly tied to full Buzzards Bay commuter rail and loss of CCCR slots at BB station. And it makes sense that it was left off the FY2017-2021 MassDOT CIP because there is so much other track work funded/scheduled those 4 years on the Cape Main & Falmouth Branch that first chance to fund a Middleboro extension & associated items won't be until the next CIP...hence these related line items being held over.
3. We know from those same threads that MassDOT's buy of the Otis Branch and pending upgrades of will open up the turning wye and derelict yard area next to the transfer station for CCCR and Mass Coastal to use as expansion space to offset the cramped confines of Hyannis Yard. Coupled with the future Cape Jct. wye that would allow them to very easily originate passenger runs at North Falmouth.
4. There are extant Falmouth Branch stations with (non-ADA) platforms at
Monument Beach and
Catumet used occasionally by CCCR excursions. The demolished stations at
Pocasset (between Monument Beach and Catumet) and
North Falmouth have land and roadside access under MassDOT ownership, allowing for new CCCR stations to be built when needed.
CCCR is going to be running a lot more Hyannis-N. Falmouth excursions in the future when that wye leg is complete...possibly even with those two endpoints becoming 'the' new dinner train route. And CCCR would be able to supplement the dinner train with more general-purpose on-Cape transit once they're free from the mandatory bridge opening and reverse move to get across Cape Jct. Things like running an RDC dinky pinging back and forth. The potential infill stop at Sagamore (or somewhere between the two bridges) thus becomes a potential transfer point between CCCR and MBTA service. North Falmouth, in addition to being beyond-the-pale for splitting Cape Flyer trains, simply is going to have lower utilization for Boston directs than Hyannis because it doesn't serve anywhere near as big a catchment and bringing the more densely-abutted Sandwich and West Barnstable intermediates online outslugs M. Beach, Pocasset, and Catumet by a huge margin. So the T will never be able to split their focus.
However, if a CCCR dinky from North Falmouth has a timed transfer at Sagamore with the Flyer you get great connectivity to both branches. All you would need for fluidly setting that up is the right track/platform configuration at Sagamore. Have a double-track turnout for the dinky to pull away and reverse direction back to N. Falmouth while the Flyer passes. Or, build a full double-track island platform so the dinky can just wait on one track for the Flyer, passengers hop across, and the Flyer departs first from the meet with the dinky either reversing back to N. Falmouth or continuing on making the next local stop at Sandwich. Such a setup would even work as a commuter rail trial. Say that Buzzards Bay becomes the new permanent terminus of the Middleboro Line, with full mainland signalization. The T could then finagle 2 morning rush skip-stop commuter extras from Hyannis + 2 evening rush outbounds within the daily limits of non-PTC dark territory on the other side of the bridge. This would in turn give CCCR a shot at pocketing some commuter revenue by running a single RDC from N. Falmouth to Sagamore timed with each of those daily Purple Line trains. All they would need to make that work as a commuter transfer service is to install cheap 1-door mini-highs at Monument Beach and Catumet for ADA compliance on the non-excursion service, and have the (presumably already built for the expanded excursion schedules) N. Falmouth and Pocasset stations done to-spec. Cheap, easy, and probably still a lot faster as a 2-seat/cross-platform trip than taking the highways to Boston.
You don't need to think big. There's a lot of stuff already in the works around current upgrades and officially-proposed, not-too-distant-future upgrades that would enable general transit on the Falmouth Branch and CCCR some nifty opportunities to expand its revenue base at low up-front cost. Playing around with the dinky scenarios...or quick trials therein...will probably serve up very useful mobility options tied to the Flyer and/or Purple Line without any need to distort the T's schedules or trainsets.