That being said,
I think it's still a small market. All of TPs I mean, new, used & yet to come (I've got a solid theory that ThinkPads may outlast the heat death of the universe, paper coming soon(tm) ). Seriously, the reason is that the used market is precisely interesting because it's cheap (it's almost a commodity market at that point) whereas the new market is becoming niche like all laptops, like desktops before — think that, for all their glory, GPUs only sell in the single-digit millions to consumers per year — no wonder the juice for these lies in enterprise.
So I think you've got room for maybe a few small businesses, small custom shops of a single to few employees, shipping worldwide of course (and I'm not a logistics expert but this is the kind of space where ideally you really want to 'shopify' directly from factory to customer because each cent will be hard fought for). Most of what people use to tweak TPs is already cheap as hell on Aliexpress or eq.
I wish it weren't so. Please tell me I''m wrong about this.