i think we have 1 of each, 1 small (hearthfire) and 1 big (dragonborn). we're already past the 1 year mark since Skyrim was released, don't think they want to devote any more time to skyrim
I am actually thinking about how much interest they might have got back into the series through Steam's holiday sales. Skyrim was constantly near the top of the best sellers list even when it was just 33% off (sadly I was silly and didn't wait and on one of the last days they had it 75% off). There very well could have been some pretty decent sales figures put out there from that sale.
Sadly with a game such as this where there is little in way for the developer to gauge their audiences continued participation (bar through forums but that is going to be an obscurely small part of the fanbase regardless) it can lead to the unknown factor. I have several friends who still religiously play Skyrim daily and would gladly buy more content provided it was good content, not just a horse. The problem is there is no way that Beth can accurately gauge these figures.
I guess the PS3 DLC sales and PC release of DB will help them to come up with some figures as to if the title is still worthy of more content or not.