"fringe platforms which can't even run a Rust compiler"

I don't know, this reasoning sound weird to me. If I make my language hard to port on ENIAC, it will most likely make it harder to port it on new platforms that behave like ENIAC, thus limiting the opportunities of building new platforms that differ from the currently supported platforms in the same way that ENIAC does.

If it's a new platform shouldn't we assume that it will behave more like current platforms than older ones? Otherwise, why do you need a new platform as the older one already exist? Of course you can say that the new platform is a variant of the older one but running much much faster, but that's only because it doesn't and its properties are custom built to support your argument. An empty set can have any property you want it to.