As is likely evident in my post on the locations to visit thread, I like the idea of hinting at their existence, but not actually feature them outright. I don't think we need to SEE them lumbering about or anything, but rather see items and structures in parts of the island that were man-made at some point. It would be interesting to see the game universe evolve much like we did and so early in the game(s) it is sort of primitive and moving towards the bronze age, where weapons armor and tech are fairly simplistic and homemade. Ad things go on they could begin to grow and adapt and learn/use stuff like steamworks or electricity or polished surfaces, and eventually work their way to a world like humans have where their technology has gone out of control and begun to really overtake their lives(not to say they're be into microchips and stuff, but somewhat like early 20th century with the dawn of fossil fuel use, manufacturing and larger populated city like areas) . But that may very well be an allegory Seith isn't keen on exploring with this series at all. (and i am talking a span of multiple generations, so this would be a VERY gradual transition across many many games.. if it happened).
either way, I like showing we exist,or existed, but we don't need to see us. Not yet.
As David said, the world we have seen so far seems to be a 'normal' fantasy world with humans/monsters replaced by animals. Having this world inhabited (or once inhabited) by humans certainly gives great opportunities for interesting large scale structures, features or areas, however I think it may be difficult to marry up the experiences of playing a mouse in a human world and a mouse in an fantasy world and that one may detract from the other, especially in a smaller production.
Despite this I am sure that if Seith wanted it could be used to great effect, (I agree that actually seeing humans in this game would not be the best) and that the hints of human civilisation could build up during the game leading to a reveal at the end of the game that allows for further exploration of the idea in a future game.
This, alongside the topic of voiced dialogue, is all up to the execution. I feel that Pulsar and evilkinggumby have both pointed out different ways of approaching (or not approaching) humans. If they do exist in the universe, I think it should be extremely subtle.
I personally feel that the game would work better without humans, but hey, I don't know what Seith has up his sleeve in terms of story!
Very thoughtful thread I must say. I can't enter into any details regarding the story, but suffice to say that you will not encounter any human beings in the game.
We won't encounter any humans on Periclave, but I wonder if there be human structures or human-made objects. I'm not hinting, b'cos I really don't know. Seith has spoken, and yet some mystery lingers...