Android no, WP7 yes. WP7 has such stringent requirements that Nokia would really only be able to make a different model for different frequency bands, and since they're going for penta-band HSPA even that wouldn't be necessary. The biggest problem with Nokia phones for years is they've held out on features, so to get the best Nokia you actually have to buy 3. I remember mono-audio only on the E62, while Xenon flash was only on the N82. We'd probably be hoping a bit too much for a Xenon flash Nokia WP7 device, but at least everything else would be included.
Nokia really wouldn't have to put all that much effort into it either - just do it as a side project, refresh it 1x per year and they'd be able to draw some solid revenue.
Ideally they'd also consolidated their Symbian line, so you can actually get a device with 12MP camera, Xenon flash, QWERTY keyboard, quality stereo speakers, and every other good feature any Nokia device has.
I'm only willing to buy Symbian if it's really cheap. I wouldn't pay money for an N8, but I was willing to buy a 5230 because of how cheap it was, and it's even better, coming close to $100, now.
Android has major fragmentation problems, it's rather like Windows Mobile used to be, with updates being uncertain. Given how Nokia treated Symbian, I'm sure they'd screw Android up badly.