i would still rather see the fantasy figures compatible with the current lines. i see a big benefit, and don't see comparison with other lines as a big liability:
my guess is that the main attraction to wf fantasy figures would be for large hordes of models. so, for large hordes of humans, it would be nice to be able to use vikings, saxons, germans, celts, numidians, and even zulus in the mix to augment the variety. several of those would also make good civilians to allow realistic numbers of townfolk as well as providing lots of options for npcs (if you are rpging vice straight wargaming) at non-heroic figure prices!
if you can pretty much mete out all your human requirements (and human-based undead) with the regular wf 28mm scaled guys, is it such a bad thing that, say, your other comapny orcs are between 5-20% bigger than the humans? even if wf put out a line of orcs, would it be a bad thing if a dozen of your other company orcs were bigger and could act as easily recognizable bosses/leaders for your hundreds of wf orcs (assuming they only sized them 5-10% bigger than humans)?
there is a problem with the smaller figures, though. if i use truescale humans, my other company goblins 'n' such get "bigger" which may not work well. other than dwarves and hobbits (which really need to be chunkier and wf would probably make, anyway), i don't feel it is a heinous compromise. also, i am kind of a fan of 15mm minis being smaller species for 28mm figures (again, except for dwarves and hobbits) -- you get that big variety and support thing; for example, if i decide my goblins are all asian themed, then i have a wide variety of 15mm options that are visually consistent and yet have noticable differences that can work for having "factions" within the goblins.