Amelia is played by a model who has very limited English and is not a very good actress. Hence why she had no lines and just had to look hot/cool in UW1 and had a few lines and just had to look hot/menacing in the prologue of UW2.
 
They don't use her because for some odd reason she is a fan favorite and they don't want to recast. It is the same reason they recast Sonja, as she was played in the flashback by an eastern European actress who could not speak English and perhaps not really act. That and Rhona Mitra looks a lot like Beckinsale (Mitra having a slightly more athletic look is the biggest difference).
 
If they do the Lucian/Kraven story they would have to incorporate Selene as she was a vampire at this point. Perhaps begin with her being turned by Viktor and exploring their creepy "father/son" unrequited-love on Selene's side-of-the-story. It also features from the images what looks like the biggest battle in the Underworld mythology which looks like it had thousands of lycans and hundreds of vampires fighting.
 
The problem with that is:
 
1) You need to get Beckinsale back, which I doubt is going to happen.
2) The battle would be much bigger (i.e. expensive) than any in UW1 or the prequel.
and
3) The actor who plays Kraven is awful. Did anyone notice that Tannis basically played Kraven's role in UW3? Viktor's treacherous right-hand man, which is how Kraven described himself in UW1 who was there in the few months that followed the event when Viktor turned Selene. He was not in this movie, because the actor who plays Tannis is much better and created a more interesting character than Kraven in UW2.
 
I say if we can get Beckinsale back, it would very definitely be the last picture she'd do in the series and I'd rather they tell a story that wraps up the Underworld universe. UW2 didn't really solve anything beyond what would happen to hybrid Markus and then stupidly killed off several new interesting characters (Tannis and Corvinus). I'd rather leave the events between the prequel and UW1 to the imagination.