I'm almost certain the characters shown off in the Legendary Edition trailer are updated models, either made for the trailer or demonstration of what the new models will look like. They have a number of telltale signs; not quite clean or detailed enough to be CGI, UE3-like lighting particularly on normal and specular maps, and mainly polygonal and texture seams/edges that are present in the original models.
Mordin's model is the biggest giveaway. It has the exact texture seam as the original, where the neck/head doesn't align with the body and the red stripe is offset a little.
But a number of the models also have improvements. They're all higher poly and have a lot of the curved edges smoothed out. The textures are all updated pretty significantly, by the looks of things, with added normal mapping for extra detail. Some new aesthetic choices too, see the specular/reflective surface on Mordin's neckguard that is not there in the original model.
They're not fancy enough for me to assume they're specialised CGI models, and have some of the original blemishes. But they're also improved over the originals in pretty obvious ways; cleaner, smoother, more detailed. I'm gonna assume these are in fact the new character models. Fancily lit for this specific trailer, but nevertheless probably representative of updated assets.