The PS3 and Xbox 360 are both superb consoles and both of them are viable options for Bethesda to release more Skyrim DLC packs, even when the next consoles are revealed.
There is no way that the company is going to stop making content for current consoles and Skyrim. The move onto the next generation consoles will be a slow one as Bethesda will not want to gamble on making a move over to the new consoles too early.
DLCs are low risk and this means that we could see more Skyrim DLCs coming our way before the company reveals Elder Scrolls 6, which could be a few years away and on the next generation consoles.
Anticipated sales of new consoles can be far off from predictions and you only have to look at the Wii U to find this out. Making content for Skyrim could be a superb way to train up those just out of school before they are let loose on a full blown game to. The heads maybe working on Elder Scrolls 6 and the DLCs may be handled by smaller teams. DLCs could continue generating income on the older consoles as Bethesda puts in another huge investment to develop a new game for new tech.
More DLCs could be a great way for Bethesda to keep fans happy until a new game is released too of course. There have been a lot of rumours about a potential Redguard DLC and bear in mind that Oblivion had 10 DLCs so we can expect more. Right now there is only three for Skyrim, these are Dawnguard, Dragonborn and Hearthfire. This means there should be plenty more to come. However personally I have doubts about there being anymore big ones. I would expect the remaining DLC (0ther than Redguard) to be similar to minor mods.