its not a case of IF its a case of WHEN
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it will happen!
i believe they will still keep to an ES single player experience but i am 99% sure there will be an ES MMORPG soon!
Pretty much this!!!
There is just far too much money to be made in MMO's for ZeniMax to ignore, especially for a game that is likely to sell millions of copies of the single player version.
I would actually love to see an ES MMORPG, providing they don't make it a WOW clone and keep the sandbox open world feel of the game. Also, they must not downgrade it to support the console crowd, if you want the MMO to work on consoles, fine go with that but don't dilute the PC version to fit inline with consoles.
At the end of the day if you don't want to play it, then just don't. I think it would be ZeniMax Online that makes it anyway with Bethesda staying on the single player version. So you will likely still get your single player fix.