The old station has about 750 spaces (it's been restriped several times). Utilization was reported as 51% (about 380/746) in 2011
, and 46% (about 353/769) in 2017
. The old station had 867 daily boardings in 2018; the new station is projected for 670 as some passengers switch to the South Coast Rail stations. Even without any extension towards the Cape, the 500 spaces should be more than plenty.
This is the station design from the 2018 Draft Supplemental Environmental Impact Report. It's probably had small modifications since then, but this is the basic design:
The potential shuttle platform is placed for nearly cross-platform transfers to South Coast Rail trains. Should it eventually be desired to bring the CapeFLYER (or non-shuttle commuter service) to this station, there's plenty of room for a new platform on the east side. However, I suspect that the CapeFLYER will never move here alone - Middleborough ridership is so minimal (less than 5 passengers per CapeFLYER train) that it's not worth the cost of even a wooden platform.