Where in the world did you hear about a 4th gen PSP?
Once the motherboard is hacked and people start testing them out, Sony will know by how many sales they get. If they get no sales because people who buy the 3000 (to mod it) don't like it and tell their friends to buy 2000s, they'll see what's wrong with the 3000 and fix it. So odds are, yeah they'll fix it.
But why bring up the topic about a PSP-4000 anyways? Worry about it when there's news about it.