I think Sabretooth has been confirmed as appearing, but I know very little about the Wolverine story. From what I'm hearing the fans want Omega Red as the main villain.
They could even get Brian Cox back as Stryker and do the whole Weapon X plot. Sabretooth was a subject of that as well as Logan.
As for Lady Deathstrike, well if the story takes place before any of the X-Men films than she can easily appear. We know that both characters have problems with their memory and have been connected to the Weapon X facility, so she could have been a former lover. That would make X2 even more tragic when Wolverine kills her, as he'd never know they were together.
In the comics Logan was in love with a Japanese girl called Mariko, and in the cartoon they merged that character with Lady Deathstrike, so it's possible the film could too.