Bethesda hasn't announced any new projects; we do know that they're working on something, just not what. TES V seems like a good guess but given that such a game hasn't even been announced its hard to speculate on when it will be released

If Bethesda is planning to release another game on the current console generation I imagine we'll probably hear about their next project soon (late summer or in the fall) and it will be released 9-15 months later. However if Bethesda has their sights on the next generation systems it could be some time before we hear about the game, let alone see it, given that Sony and Microsoft haven't even announced new systems.
If you'd like to speculate about the game, or read other's speculations, we have an official thrad for such things http://www.gamesas.com/index.php?/topic/1098899-official-tes-v-speculation-thread-39/