In the early models, with the staggered wheels, there were literally four different ones, so even discounting the F/R size differences, you couldn't swap them side to side either (and, the tires are directional, too). At least with the winter tires, you can swap F/R, but would have to remount them to swap sides so that the rotational direction was correct. FWIW, when they were delivered, the set had all mounted for the left hand side! Before I could take them home, the dealer had to swap two of them (came direct from BMW that way).
Wider tires are more prone to aquaplaning, and, if all-seasons, in the snow, won't have as much traction. Some cars give you lots of options, the i3 was optimized, and those options fell away without more changes.
2011 535i x-drive GT, 2014 i3 BEV