Like wolves with dogs, I think it would be interesting to be able to crossbreed sylestis that are similar to each other. Like the Lupora with Zolnixi, since they are both canines, for example.

Given that traits vary from species to species, I don't think this would be viable.

Because of the different traits, I don't think this is possible. However, I still think an interesting alternative would be to craft chimeras by combining different essences. Perhaps closely related species like a zolnixi and lupora would be easier to combine. More distantly related sylesties would require other materials. I don't know if realistically it would be possible to cover every combo though I do think it'd be neat if there were some that required multiple different species' essences to create more complex new species.