I would have preferred having oz return a character in general again instead of introducing Kennedy as I don't quite like or even enjoy her as a character or the fact that Willow would move on from 'Tara' (although I like her.. I'm not a big T/W shipper) so quickly after she nearly destroyed the world for her. It always just felt as if Joss had to rush over the heartache. I would have understood if she took comfort in Xander or Oz. They've just always been her support base but I suppose it's just me...
I definitely think that would have been a much better storyline than the whole romance between Willow and Kennedy. I was and am a huge fan of Willow and Tara's relationship and I feel like Willow moved on too quickly from Tara's death (even though the exact amount of months is not known). I also didn't like Kennedy's character at all- she was bossy, snobbish, and didn't seem like a good fit for Willow. In the 7th season of Buffy they ended up bringing back a lot of characters, even just for cameos (the mayor, faith, Drusilla) so I was disappointed when Oz wasn't among them. I also was a huge fan of Willow and Oz's relationship and, although it still would have been hard seeing her move on from Tara in time that feels so short, I think I would have preferred it. Plus Oz was just an amazing character that I wanted to stick around even if he wasn't dating anyone.
I would have liked that, though she was 100% lesbian. I would have liked his character to have appeared and ended up with Willow instead of Kennedy ending up with her, I cannot stand her character, she's just so annoying. I really wanted her to die.
I would have liked it, if they'd have been able to get Seth Green back - I'm not sure they could.
And it wouldn't have worked because of the way they handled Willow's sexuality. They should have had her realising she was bi, instead of declaring herself gay. Because of what they did, any return of Oz - or any male love interest - would have been like retconning that entire move.