Second Windga would be hilarious!
I think the II versions of a melee skill should flat out replace it(that's how a certain other MMO does it...); I don't see a point in needing to use Second Wind I if I have Second Windga, but of course, there are those who do, so I imagine the "upgrade-replaces-old system" would have to allow you to set the old skill to your bar also. Maybe it could just have a different icon?