I suspect Pro owners will replace on roughly the same cycle as the standard iPad.....maybe even more often. As a consumer group, Pro buyers are more likely to be attracted to technology improvements and be early adopters of the latest device. So, they will tend to replace their iPads more often.....as a general rule. YMMV.
I think this is a good point. Pro users tend to not be satisfied with older technology, and will likely upgrade as fast or faster than non-Pro users even if they aren’t forced to by laggy performance. I’m also guessing a Pro iPad might add another year or so of life compared to the non-Pro iPad. I can’t imagine going much past 5 years of IOS upgrades, even for a Pro.