Here's a summary of what we already knew in May:
Microsoft is actively working on a v2, and it's already being tested internally.
Microsoft Band v2 will be thinner and better form fitting (could have a curved screen).
Microsoft Band v2 will be tougher (a scratch-resistant screen, a battery junction that doesn't corrode, new clasp design, and possibly a different material covering the sensors)
Microsoft Band v2 will introduce new functionality, expose new sensors, and will eventually be part of the Windows 10 family (through software improvements and updates)
Additionally, I'm hearing that Microsoft Band v2 will be waterproof and there are whole slew of new integrations and different activity tiles coming.
All of these improvements (and more surprises) come, in part, from user feedback. If you're a Microsoft Band owner and would love to get your own suggestions recognized, there's a couple official ways to do it: