Being able to keep the same keyboard would indeed be great, but Apple never said that the current keyboard will be working with future iPad Pros.
Also, given the nature of the keyboard (being so tightly coupled to the dimensions of the iPad) it was to be expected that compatibility would be broken sooner or later.
So yeah, it's unfortunate, but I don't think Apple is doing something evil here.
Also, on a side note, I cannot really empathize with people being offended by a higher than expected cost of upgrade while they are ok spending 2000$ for a tablet/keyboard combo. If spending 200$ more (by selling old keyboard and buying the new one) is a deal breaker to you, then you should be looking at an iPad Air with a Logitech keyboard instead of going the fancy iPad Pro route.
Also, given the nature of the keyboard (being so tightly coupled to the dimensions of the iPad) it was to be expected that compatibility would be broken sooner or later.
So yeah, it's unfortunate, but I don't think Apple is doing something evil here.
Also, on a side note, I cannot really empathize with people being offended by a higher than expected cost of upgrade while they are ok spending 2000$ for a tablet/keyboard combo. If spending 200$ more (by selling old keyboard and buying the new one) is a deal breaker to you, then you should be looking at an iPad Air with a Logitech keyboard instead of going the fancy iPad Pro route.