I wouldn't have a problem with it at all if they went about it the right way. Im not sure i've ever "shipped" him with anyone other than Misty. If they ended up together it wouldn't feel forced at all to me, given their past. I always saw May and Dawn as little sister-figures to him. Iris is just kind of a friend. None of them would have a smooth transition into a bf/gf relationship status for me. Putting him together with one-shot crushes would especially feel rushed. I guess what im saying is for me personally the only girl I could see him being with, without it being rushed and awkward, is Misty.
I still think the writers could pull it off without taking the focus off of his journey. It doesn't have to be a huge deal. It could just be an episode or 2 focusing on him getting together with whoever it may be, then you could leave it alone for the most part..unless it was someone he was traveling with like Iris..then it might get awkward.
So yes. If the transition is smooth enough and it isn't forced or awkward I think he should. Misty would be great but whoever fits the criteria I mentioned would be fine with me.