For one, silent protagonists are a dead archetype. Thankfully, it seems BioWare has finally come to this conclusion and discarded any chance of ever having a dumbfounded main character awkwardly staring at everybody else while they talk for 50 hours.
Secondly, multi-race selection with multiple backgrounds is bad for game development and storytelling. When there are so many variables and possibilities to consider, it dilutes and cheapens the overall story. The reason Shepard's story and even Hawke's story were so engaging is because they were more defined. However, in that definition, we also had more flexibility to shape their personality.
You can't do that with a silent protagonist or a main character who can be four different races with a dozen different backgrounds. There's just too many variables and not enough defined points. Giving players more choice and freedom negatively impacts the overall game and the story BioWare can create.
Thus, I believe the next protagonist in DA4 needs to be more akin to Shepard/Hawke and less so to the Inquisitor/HoF.
Thas gewd, thas gewd, mang. You feel however you want, and you can do whatever you want in your own Dragon Age Keep. But don't you dare take away my choice of protagonists. Hawke was about as deep as a mud puddle on a concrete sidewalk. The story was even more "black and white," "option one or two," than DAI is. And that's saying something. This means that's pretty much how Hawke is, too. He either hates mages everywhere always, or he loves mages everywhere always. Except blood mages, which he hates everywhere always, anyway.
I've spent over 600 hours in DA:O. Over 600. Yeah, that's a lot. And I did it more or less during one summer at college, too. Why? Because I loved it. I loved the story, the way things panned out, how my choices affected the world around me, the endings, just.. everything. To me the "silent" protagonist wasn't actually silent, they just didn't have a voice actor, and I was okay with that. The protagonists in DA:O weren't silent, they talked, they stated their opinion, they flirted, they loved, they laughed, and they lived. Just because you couldn't hear it doesn't mean they were silent, because you sure could read it. You want a silent protagonist? Look up Fable 1 guy. The extent of his interaction is pelvic thrusts, farts, and "come hither" looks. Your choices in that game are only in what quest cards you pick up and whether or not you murder a town to buy all the houses and have everyone pay rent to you.
If they had the Keep around during DA:O they could have easily handled everyone's unmodded stories and choices in there and it would have progressed into DA2 seamlessly, thus even possibly allowing an unmodded warden to show up at some point for a cameo. But, unfortunately, they didn't. With it now, however, there is no purpose of having "a Shepard" in the DA franchise. We've already got that, Hawke. I'd rather stick with limited options of player characters and choose them in my Keep than have another character like that. If I want a Lavellan or a Cadash to appear in my next DA, then that's what I should get. If it were entirely Bioware's/EA's story there would be no options and no need for a keep. But it's not, it's as much mine as it is theirs, thus is why they implemented the keep.
So, again, I reiterate, don't go around saying there needs to be "a Shepard" in the next Dragon Age. There doesn't. Dragon Age is not ME. They started the ME series out that way, so it made sense to keep it that way until the end. DA, however, was not started that way. We've already toyed with going that route with Hawke, it didn't work too well. In DA you can be more or less whomever you want to be and make whomever you want the important character of that game. With the addition of the Keep it's even easier to keep all the important details down.
So, in conclusion, I get it, you want Hawke, or someone like them, to be the big kahuna across all your games. Maybe you'll have a chance to do that. For your sake I sincerely hope so. Yet that doesn't mean we all want that. So why limit what others get, why limit the Keep and its functionality? I say nay to your assertion that we need "a Shepard" for the remaining, or even the next, DA.