I figured given the size of the trd 19's, in both height and width, that larger tires would work up to a certain point. I've toyed with going as big as a 225/60/16. But 215/55/16 would fit no problem I'd guess.The size on the xB now are 205's,going to 215's is what I'm thinking of. Tread wear might be a problem if the wheels aren't wide enough to keep the tires' profile correct on the road. If not, the tires would draw and keep the tread contacting equally all across the width of the tread. Also, the more rubber on the road might reduce MPG.
When it comes time to swap the summer wheels on, and if I have a 225/60/16 around, I might try one just for the heck of it.
I've toyed with the idea of going to the white wall look full time on bags, and I'd want to tuck a larger tire more looking like an old hot rod, that size would fit the bill and is also available in WWW.