If it'll bring Kathy back, if only briefly, then it's all to the good. I expect this was thought up when Letitia Dean said she was going to walk... it gives Den a connection to the old-school Square he doesn't really have with Vicky or Dennis or Chrissie. Without Sharon, the Watts' don't feel like one of the classic rooted set, rather like a freshly created bunch for dramatic purpose. Plus, it gives Dennis a character to spar with when the godawful 'Shannis' is put to rest (discovering he has a brother, sibling rivalry, etc -- even if it is Ian). Plus, it gives Pauline another reason to stare daggers at Den, as Ian is the only member of her family who is alive and present who he hasn't corrupted. Well, except Martin.
I'd like to see Kathy back. And it is conceivable that she and Den did the dodgy way back when, considering the player he was back then, he did shag his best mate's [Pete] neice, so why not his wife. Well it would have been his girlfriend... I think Kathy had Ian when she was 16 or 17, and we all know that Den like's them that age.
*cough* Michelle *cough*. *cough* Zoe *cough*.