Beamish started off with the Town setting in 1913, then went back a bit for the agriculture / farming [I can't recall the exact dates atm] in a couple of areas. The most recent area to open is the 1950s. I can see them considering another time jump in the future ...
It has the Pockerley Waggonway, a short bit of standard gauge as well as some narrow gauge.
Plus the tramway circuit, of course. Now includes some buses. I think they are giving up on the trolleybus.
Which are all part of experiencing history.
However, I get the impression that exhibits often have to work for their living ... and that can be hard on older [restored] items.
Much like some heritage railways and even the current mainline system that all activity requires the items receive suitable / preventative / routine maintenance.
They're only just building the 50's part now, as it slips from something you can ask your grandparents about, to something you can only read about, so that gives you some idea of how they like to do things.
The working items as well as humans in period costume bring the museum to life, that being the selling point. It is a living museum, so there's no information boards or interpretation paraganalia (bar the map and guidebook, an essential). You just walk through and experience it.
But as such, static displays and the general vibe, matters just as much as working items, and operation is by no means essential. One of the best times to visit, is when there's not much on, and thus little being operated - it means there's less kids and generic tourists getting in the way of you and the experience. In some respects, quite literally. And with a good experience, comes lots of discretionary spending. Especially since the ticket is actually an annual pass.
They are also not a transport museum in the sense of restoration/preservation, although there is a transport sub-group for that purpose. They can and do run replicas, if it adds to the experience. They don't care if vehicles only run a few hundred yards in arbitrary manner - the steam branch line literally does just that, just a run up a line from the station and then back, as does the waggonway.
In that respect, it's more of a scene based affair, and you suspect they only wired a full loop for trams for their practical use to transport visitors and/or give them a decent view of the whole site, which is quite large, rather than seeking an authentic experience of trams (although as said, the authenticity of operation, such as uniforms, is also important).
That's why they don't particularly mind having trams from wildly different eras calling at the same stops, while vehicles from yet more eras also run past. There is always a part of the site where they fit.
They have a giant stores, so they hoarded plenty of items over the years to now display for this latest 50s period, items such as crockery etc.
So there's the issue for Beamish. One day they might wish to build an 80s area (although the available space might be an issue - the only reason I can see why the 50s area is literally next to the original town, is space).
But do they have the space to store a MetroCar, and would they want the expense of ensuring it could run? I think not. I think they'd prefer to go the route of either a static mockup or some kind of replica, for which quite obviously, having an original unit would be desireable.
Never mind ensuring the unit can run, it would be a stretch to build the infrastructure necessary, only to run it a few hundred yards in and out of one station as part of an 80s scene, most likely a council estate, with houses and a corner shop, maybe a Chinese take away. Some NBC/PTE buses and stops. A time of optimism, before everything went into decline.
So therefore I do hope someone at Nexus, as the custodians of this social and physical history, has been smart enough to ensure that a unit has been kept, perhaps one that's suffered a terminal failure, not for immediate display at a museum, but long term storage, preferably in their own secure areas.
Because if Beamish ever wants it, on current evidence, they're not going to be asking for it until say 2050, and won't be bothered if it's a non-runner and cannot be made to run again (under it's own power). They might only want to make the doors operational, replicate the original sound and feel. And this will probably only be after they have somehow found a way to expand the site.
Obviously the dream would be a short stretch of straight track, from an "underground" station to one of the suburban stations, both the "new" (and thus most 80s Metroish) style. As they have done with other areas, Beamish typicay waits until a building is about to be demolished, and then takes it brick by brick, to be rebuilt on site.
So there's another issue. Will Nexus ever actually upgrade the Metro by completely rebuilding the "new" stations, the ones built from prefab concrete and steel work? Probably not.
It will all be down to Nexus. So don't hold your breath I'd say.