A few thoughts :
I have an Olympus OM2-SP (Spot/Program) SLR dating from the mid-1980s. It is black, and I was very lucky to find such a mint example on eBay in perfect working order. It is a Beautiful Thing (TM). I caress it and admire it. Owning it, and the 50mm f/1.2 lens and the 55mm f/1.2 lens, makes me Happy. It's about 27 years old and mint, as is the 50/1.2.
I am also lucky enough to own a 5D3 and a 7D. The 5D3 especially is also a Beautiful Thing. It actually makes the 7D feel plasticky! And the 7D is NOT plasticky!
But in 27 years' time, apart from the fact that I'll be dead, will the 5D3 be usable? Unfortunately, I fear not. I doubt that USB will be around in any compatible form, or indeed compatible card-readers.
On the other hand, although 35mm film, and will by then be a rare commodity indeed, and processing services more so, I expect that film SLRs will still be usable, for those who really want to use them.
The film SLR could in a sense be seen as an "heirloom". Maybe not so much for an Olympus camera, but consider a Leica M-series rangefinder film camera. They are heirlooms. The M9? No, it can't be; it won't have the necessary longevity, I fear.
I find this all rather depressing. The 5D3 and the M9 and so on are wonderful, high-quality pieces of engineering, but they seem doomed to be ephemeral.
I don't REQUIRE my 5D3 to last many years; if I'm still around and into photography and still cashed up in 4 years' time, no doubt I'll buy a successor, but that's not the point I'm making. It seems a shame that such wonderful things won't last 20, 30, 50 years and still be usable by most people.
(I'm just old and sad!)