If GRRM dies before the next book, they might not have a season worth of stuff.
He does need to get going a bit, but there is also plenty of material left to go a few seasons all ready I'd think.
I didn't think any of it after 3 became boring personally, just starts getting a little more focused here and there, IMHO.
They may well start combining a bit of things later, you're right they'll probably have to or the entire series would get odd and all discordant, but there is a lot they could do along those lines.
Might get even more interesting just to see how they do it as they usually don't diverge from the books layouts too radically.
There is still a lot of meat in books 4 and 5 that things can be done with, I think if you weed between the too and lay them out you can really stay true to them and make it very interesting.