For me, a pro dancer would be the wrong choice for the main presenter, whomever they were. That's for two primary reasons. First, there would surely be an overwhelming temptation for them to chip is their two penn'orth, which isn't what they would be there for (I know that there are people who will say that Bruce does this, but I think he's relatively restrained about it and imagine how much worse it would be with an opinionated pro dancer). Second, carrying a two hour live show needs a seasoned TV professional, it's certainly not a job for a debutant.
Should Bruce ever be replaced, they need somebody with similar credentials: an experienced host of unscripted live TV with a good knowledge of dance. A tough brief to meet.