It'd depend entirely on the level of support a competitor offers, right? I mean that's why RPi is still so popular despite there having been a number of ARM competitors offering more power per dollar for like a decade now. The strong software support led to a strong community/overall ecosystem, which has led to a strong install base, which further improved the community and ecosystem.
It's a combination of first mover advantage with continued strong software support that keeps them so prominent as-is. I don't see why a different ISA would fundamentally change that formula.