Or more? Like you wander through grass, caves etc to find Pokemon but they can come in groups. Would that be too big of a change to fight with a team of 4 (or less) against (at the most) 7? Just keep the trainer battles the same. A 6 vs 6 duel seems too chaotic.
No. As much as I like large battles, they'd be too gimmicky and someone would quickly find a way to get Earthquake, Heat Wave, Discharge, and Surf on the same team and wreck all the things in one turn.