I think it depends on the market. Right now the biggest market is 1080p, so that is their biggest priority. Yes, they are working on higher resolutions so not to miss the market change, but until higher resolutions go from enthusiast to mainstream, they will be a future tech.
Directly to your question though. I believe it possible, but unlikely. Not for design or tech limitations, but because as I said above, the market isn't truly yet demanding it. If 4k TV's and monitors become the norm and prices drop sufficiently, we will likely see a burst in GPU horsepower.
At this time, there is no downside leaving 4k to crossifre/sli setups. Just boosts their sale a bit.