It is explicitly less elegant for commuter rail, and even moreso for the densest inner regions seeing 15 min. headways. There is a minor door-opening delay while the bridge plate pops out at an upward angle (up-and-out so as not to uselessly strike the side of the platform and require manual resetting) and lowers itself in place. And it does require onsite staff assistance, because a wrong step to the sides of the bridge plate sends you or your belongings into the gap. It's appropriate for Amtrak where there's higher degree of staff assistance, often an available station attendant able to pitch in on additional doors, and far fewer boardings/alightings at minor intermediate stations vs. big city-center stations that are more likely to have the track separation from freights and the budgeting + traffic levels to do full-edged no-gap platforms from the get-go. RUR's still going to have multiple onboard conductors because of FRA regulations governing crew rank (i.e. lead conductors do safety checks and have direct supervisory authority over the engineer), but for efficiency's sake they're going to need to be more ruthlessly managed to keep spare staffings (esp. for any assistant conductors that can be pared from overstaffed trains) to a minimum. That goes out the window if they all have to be door helpers for minding the gap.From the Amtrak thread, the idea of a train carrying its own gap-filler so as to operate on high level platforms (single-level, high-platform coaches are a key part of RUR's plan to shorten dwell times) on freight clearance routes.
F-Line's example is from Florida East Coast RR (the freight RR that owns the tracks, and would not permit their freight ops to be spoiled by their child-later-spun-out Brightline (now Virgin))
E.g. on the Lowell line (and on all routes into Maine (Downeaster) and NH (if it happens)) this would have been a elegant solution at Winchester Center, and then applicable at Wedgmere and critically, would allow a simple 2 track CR tunnel (or 2 CR & 2 GL) at West Medford,
It is a possible very very very last resort for any lines that simply cannot have their platforms raised gapless. Haverhill Line on the Pan Am freight main, for instance, is never going to be able to do more than retractable-edge mini-highs at Ballardvale and Andover (which are not abandonable stops, being in vibrant village centers) because their positions direct-abutting grade crossings rule out freight gauntlet tracks. Haverhill Station may also have a problem there accepting a gauntlet because of the adjacent install of guard rail on the Merrimack River Bridge approach. That may be the very last schedule on the whole system that still has to flip door traps after the other malingerers have all been stamped out. I'm not sure just one single outlier that already manages to have full ADA-compliant mini-highs is going to justify the fleet purchase of auto bridge plates (they are a little maint-intensive for icy climates, even when rarely used). And it's certainly not going to be worth it for keeping a Wedgemere or Mishawum on an Urban Rail schedule; it's bad if stations that small/redundant are consigned to the highest-end dwell outliers needing the most staff assistance around the gaps. Starts undercutting the principles of what Regional Rail is to start expanding the range of exceptions (esp. if they're optional like those two Lowell Line zits).
The purchase Amtrak (and VIA...and Virgin) is making is very right-sized for corridor intercity. Much denser than that...bleh, starts getting to be a real ops impediment to have gapped platforms on a commuter run. I can definitely see all the Downeaster platforms in NH & ME (excepting gap-filled Portland) getting lengthened w/gaps after the new cars...and maybe they try extra-special hard at Haverhill because it's a combo DE stop or drop it altogether from the DE schedule or swap it with full-high Lawrence for platforming consistency on the route. But it's not really going to be a strategic consideration anywhere for the MBTA, including on the other freight-clearance routes (outer-Worcester, inner-Franklin, all-Lowell) where RUR service volumes will demand gap-free platforms and nearly all affected stations within those clearance territories have plausible solves for getting there.