Although it would certainly be a complicated and expensive project, has there been any progress at all regarding rebuilding Walpole station?
No...nothing started at so much as the conceptual level because it's such a high-difficulty one, and because Town of Walpole tends to be very hostile to deal with on any sort of community input process so it figures to be slow/painful going anyway. Franklin Station was first on the list of priority ADA jobs on the Franklin Line, as knocking out commuter rail's #3 highest-ridership non-ADA stop (Walpole being #2 and to-be-ADA'd Natick #1) would take some pressure off.
Unfortunately there are very few possibilities that would keep the
historic old station depot building in-use. The current platform pinned in by the Foxboro wye is only 4 cars long, the depot is massed up against the tracks preventing a full-high interface with the building, and mini-highs at
either end wouldn't work because of building interference or interference with the wye track's clearance envelope. So the only ways to ADA it in place end up
shortening the platform to 3 cars by either backing away from the building or the wye. Plus the current location cannot serve both Forge Park and Foxboro directions at once, with the depot parking lot grade crossing making any offset Foxboro platforms just as hopelessly short.
The only way to effectively do this is move the whole station away from the depot and re-center it over Elm St. Widen the
double-track bridges over Elm and the Neponset River to quad-track equivalents by eating the side path to the depot building. The widening, which just eats a couple trees between the main station parking lot, allows for a full-high island platform bookending 2 mainline tracks and the northbound freight wye turnout running extra to the side. As a full-regulation 800-footer the platform would run approximately from the corner of the International Paper Building (about where the "T" sign is on the side path in Street View) to a point about 6 parking spaces back from the rear corner of the main lot. Primary egress would be under the Elm bridge on a widened sidewalk, with secondary up-and-over egress possible from the back of the main lot and/or the back of the CVS plaza on the corner of East & Main. Trailing crossover tied into the Foxboro wye switch would allow access to/from Foxboro from either side of the island. And the single-track switch coming out of the downtown tunnel south portal would divide into 3 for turning out Framingham freights on the northbound wye ahead of the station as well as let passenger trains pick either side of the island.
That's probably the most service-robust way to do it, and other than some fairly trivial EIS'ing at the Neponset crossing adjacent to Elm it affects basically nothing with the surroundings. It's a highish price tag relative to other station accessibility projects because the bridge mods are significant and the ADA entrance at Elm may need to include an elevator if ramp interface ends up being difficult (though you should have ample room for a switchback sticking off the southerly tip of the platform). But given that the stop does nearly 1000 daily boardings and would explode in a big way with RUR service levels and new bus routes feeding it from the north out of Medfield/Millis the budget is right in-line with what you'd expect for a showcase-ridership stop. However, any which way expect Town of Walpole to be utterly infuriating to work with and reject nearly anything presented to them on first look...even the stuff that's unequivocally good for them. It'll be howls of bloody murder that the depot building can't continue being 'the' train station, even with that being more or less physically impossible. They own it and have no shortage of re-use opportunities with it being a stone's throw away from the new stop...but the T is almost going to have to outwait their demands of the physically impossible before they calm down enough to bargain on anything. I wouldn't call it NIMBY per se since they're pro-transit, but local attitudes trend to shrill irrationality in a very NIMBY-like way so that's the primary impediment to getting something done.