Don't worry, I completely understand being a bit pessimistic about carrier updates.
After doing some digging on how long it took the One M7 to get the Sense 6 update, it seems you may be partially right. The developer edition of the M7 got it about 2 months later. However, the carrier versions quickly followed. TMo, Sprint, and Verizon got it about 2 weeks after the DE. AT&T took about a month after the DE. In any case, HTC met their 90-day deadline by a pretty large margin.
So, if HTC and the carriers follow this same route (no guarantee, of course), we should hopefully see Sense 7 on the carrier models by late May/early June.