Maybe varying degrees of paralysis and burning would be nice, but nothing else.
-pokemon evolve in mid-battle no
-trainers get exp from beating your pokemon (don't exaclt know how it would perfectly work) it would be weird
-trainer pokemon have EVS (i used an AR code to catch one, it had 0 EVS) would that effect much?
-game won't say what pokemon trainer is sending out but you can still switch (unlike "set" option) pretty cool idea
-smarter trainer pokemon I've been dying for this to happen!