I remember I read somewhere, though I can't find it anymore, that Todd Howard (or someone else from BGS), said they would keep updating Skyrim as long as it is played.

Do you think we have some responsability in the level of awesomeness that Skyrim will ultimately reach ? That is, do you think that if we show or commitment to the series and keep playing Skyrim, and advertising it to our friends and to the surrounding people, leading to a Skyrim activity which stays high on Steam as well as on the official Forums, then the official, that is modless, game will ultimately get even better. Could it lead to more DLCs and more features freely added through updates?

Besides, do you think that through sharing our ideas in the DLC suggestion threads, or for the more talented (among which I am not) through implementing it in mods, we can contribute to make the said updates, DLCs or expansions better, by ensuring that the Devs have as many ideas as possible at their disposal (which is good since when ideas meet, they make babies, some of which can be awesome)?

Skyrim will only be supported as long as BGS is willing, which is not necessarily how long the playerbase keeps playing. There are people who still play Morrowind up to this day, and there is no update for that.

Or, God forbid, multicore support for Oblivion. Oh Talos, I'll play that game again if it supports multicore

Well as much as I like their thoughts if it's true, somewhat I still hope they don't cling to Skyrim forever. It's a good game, what the hell, one of the best out there, but it has been nearly a year now, and some thoughts have to be focused towards new TES. Ofcourse, by that, I don't mean they should start working on it right away. Two years, three perhaps untill they release new TES would be just fine.
But yeah, I fear if that's true new TES might be on hold, and I doubt many of us would like it. So I would like to stick around with current ideas, 5 DLCs (Or 6 was it?) few small, few big and then lets set sails to the new TES.

Todd says a lot of things that are either temporarily true or notable for an absence of fact.

They will make Fallout 4 first.

The bottom line is money and profits and there is only so much of that to be squeezed out of the one game -a balancing act id guess between keeping enough people interested to publicise the next one on the horizon and they do that by DLC, so how long? who knows depends on so many external factors too like the world economy and sale prosepects
I personally would guess enough substantial DLC for the next 2 years and a lead in time for the next TES then of another 2 years but its like second guessing the lottery numbers.