In current mobile market, with Apple, Android, and WP7 looming? I honestly doubt it would have been a bright future regardless of agreement with Microsoft. I am afraid the latter just killed Symbian a year (or so) earlier.
Well, relatively speaking. It seemed like Nokia was actively courting developers. See:
Nokia Calling All Innovators Ironically the deadline for this promo isn't even over yet! This is (was?) a North American specific program. AT&T was involved, to me at least it looked like Nokia was finally taking the North American market seriously and with AT&T on board it also seemed as if they found a carrier partner.