My kneejerk reaction was that, from a programming standpoint, offering the ability to renumber measures ought to be a piece of Cake.
Then I thought about for 5 more seconds, and realized that such a change could be a much bigger deal that you might imagine. The kind of "simple" change that destabilizes the code for months.
Think about how many places in the program measures are referenced, such as the Paste and Split dialogs. Think about the ramifications of importing Broadcast Wave files. How would it affect CAL scripts? Groove clips? Where do your markers go when you redefine the base measure? Do audio clips automatically slide over to follow?
I'm not surprised they're in no hurry to jump on this one.
Still, it would be a nice feature.