It's lame and cliche' as Hell. That kind of self-importance may have worked in Knights of the Old Republic, and to a lesser degree, Morrowind, but the Elder Scrolls hero should be an anonymous and mysterious agent not publicly tied in any overt way to the big political movers and shakers.
I wouldn't mind there being a new Emperor or Emperor to Be in the next game, but if the player interacts with him at all it should be as an errand boy, and not even to the extent you were an errand boy to Martin in TES IV, but on a far less personal scale.
Agreed, I think after Oblivion people are tired of being forced be an Imperial Lapdog. In Morrowind you were largely left with the choice to either follow the Empire or just simply tolerate it. Oblivion tried too much to make the Empire the ultimate in good and righteousness, although this is somewhat justified as any empire will have the highest support for it in it's heartland. I'd like to see a more dynamic ability to affect the story, like in Daggerfall where you had multiple endings, or even in Morrowind where you could choose whether or not you wished to kill the Tribunal.
By that note, agents such as the Tribunal and Nerervarine could make a claim to imperial throne by proxy of having "divine origins" although this is unrealistic as I doubt any of them would have a desire to ascend such a throne (only Dagoth Ur really had such a vision), and after Lorkhan's Heart being destroyed their divinity is pretty much fading out.
The real question I have that I couldn't fully understand is that while Martin's sacrifice closed back the jaws of Oblivion, what now enforces the magical barrier between Nirn and the realms of Oblivion? Is it Martin's Soul that now stands as a monument in the Temple of the One? I really am unsure what protections are there.....
I would like to see a more tumultuous climate in the next TES, so placing it not long after the events in Oblivion is fine with me, like just a few years or so. I'd like to see a lot of conflict arise due to the lack of an heir to the Imperial Throne, but not from a front-seat view, I like the events of the Imperial Government to play out in the background and not be the primary focus for the game.