I don't think cohesiveness across these systems needs to be a prereq. In classic mode things should work great. In Metro mode things should work great. Bumpiness in transition, IMO, is acceptable for v1.
To put it another way, I'd much rather have bumpiness shipped on day X rather than a delay to clear up all the transition bumpiness and ship 6 months after X. Although I'd like to see updates that fix the transitions come out a 8-12 months after release.