Actually it still wouldn't be used because the opportunity cost would still be way too high.What kills Mega Audino's chance of being useful is its Ability. Healer just isn't that good, especially when compared to normal Audion's Regenerator (also Audino gets Heal Bell). It's also slow. However if they give Mega Audino the new Triage Ability and if Triage works on Heal Pulse...
In a vacuum, yeah, it'd be good and useful... but we don't live in a vacuum. We live in a metagame where using Mega Audino means you can't use Mega Salamence.