I think just understanding why Pixels are the only supported device will answer every question about "Will X phone be supported".
Beyond that, it seems that just dealing with one brand of phone is enough work for the devs. They're also looking at producing their own OEM phone sometime later, so I highly doubt throwing in another brand of phone is really feasible.
Even if Jolla used the titan chip like Pixels, there would be so many little differences that I would expect a pretty large workload would come from it.
Jolla doesn't even have global support yet.