Yes, there are rumours from things Joe Q has said that have led people to think there will be a fifth ongoing. It's possible someone misheard him say the Ultimate line has five titles a month (UF4, UXM, ULT, USM, and whatever mini, at the moment, the Ultimate Galactus trilogy) and misconstrued it as "five ongoing titles a month".
If there is a fifth ongoing, I'd love it if it were a character who isn't as big in the 616 universe as in the Ultimate universe, i.e. Captain Mahr-Vell.
I've heard Q mention stuff here and there about a fifth title, but I always assumed he was just talking about whatever mini was going on at the time. I don't know... It would be cool to see a fifth Ultimate book.
I think the title should be another single character. For example, as Bass said, Captain Marvel would be a really cool person to dive into.
Bottom line is no fifth Ultimate ongoing title has been announced, or even rumored at, otherwise I'm sure we'd have heard about it here. As a matter of fact, I remember someone from Marvel saying they were keeping it JUST the 4 ongoing titles with the occasional mini-series. And once Ultimates 2 is over, we'll be down to only three ongoing for awhile until Ultimates 3 starts. I'm 99.9% positive at this time there are no plans for another ongoing Ultimate title. This could, of course, change at any point, but for now thats how it stands.
If there were to be a fifth, I'm with Bass, it should be someone we don't see enough of in the 616 continuity.
There have to be thousands of tragically underused characters, we don't need more Daredevil or Punisher for example.
There are a lot of aspects to a world, so far each of the titles have their very strict domains. It's defining a new domain and getting a character to fit into it that would really make a difference to the universe, not just another crime figure, or another alien, or another mutant or another explorer.
I made this comment in another thread but it really does belong here. The way I see it, if Marvel sticks to their mode of operations with how they've been rolling out the Ultimate line, my bet is that sooner or later they'll be releasing a series with a focus on magick, as they have covered every other base at this point (Accidental superhero - Spiderman, mutants - Xmen, Superhuman super group - Ultimates). My bet is a Dr Strange or perhaps Ghost Rider title (depending on how well the movie does).
I think magic should be very low key in the UU. Stephen Strange (jnr) isn't very good at what he's doing, and he probably uses all manner of eastern hallucinogens to achieve his goals, this will play a large part in the ambiguity of magic.
I'm a firm believer that a good mystery should not be ruined by solutions, by having a magic based book we will be forced o examine how it all works, and should this happen we shall undoubtedly find an unsatisfactory solution.
For example, you say a spell, who is the spell to, who made up the words, how is contact made, where did those one is saying the spell to come from.. a whole host of problems arise.
This said, something more 'spiritual' or religious is something that could be explored, but this will probably appeal to only a few and I only suggest it because it's something that i have personal interest in.