There were no proposed ideas for a new series after ENT.
There's a ton of stuff they could do, proposed around here - alien-centric series, Fall of the Federation, another stab (more accurate this time) at Birth of the Federation, Fed Civil War, post-Dom-War, Eugenics War Era, planet-based, Earth-based, far-flung future, anthology, even time travel or Academy based though those are often cited as ideas nobody should ever, ever do.
The jury is way out on whether CBS has any interest in doing another series. If they did, it would only be because of the interest spawned by JJ Abrams' success.
Yes, excluding all temporal precedents is certainly that easy.
See the TNG ep Parallels.
Time travel in Trek has no internal consistency so any type of story is possible. I just describe the Trek XI situation as parallel realities rather than timelines. The time travel stories are within a single timeline, but that's not what Trek XI is about. See? Problem solved.
TOS was about exploration, about going boldly where no man had gone before.
The funny thing is, it wasn't. It was about the Feds playing Space Soldier and Space Cop for the Federation and its interests; doing some diplomacy; having some personal adventures unrelated to their job description; and doing some exploration (often with the goal of either correcting Fed blunders, inducting new members into the Federation, gaining important contacts for the Federation, often related to resources, and the like).
Really, TOS was: Kirk & the gang go boldly to serve Fed interests, expand Fed power, fend of Fed enemies, protect Fed colonies and outposts, and chart some nebulae in their spare time. This may not sound as romantic as exploration for its own sake, but having the Federation serve as the rationale for most of the stories is a strong organizing principle. I'd like to see the next series, for example, return to the long-neglected role of Starfleet as the Federations' cops.