The idea isn't bad but
auto team balance would be the most hated feature then
.
It could count wins instead, would need 5 per map to be applicable for the bonus, could work.
Regarding matches dragging out, if the map ends in a draw - or plays the full map change time - no one gets a bonus.
It'd be best if Auto Team Balance was absolute in terms of mixing up the teams though, e.g. never splitting up banners of more than X (3/4), thus always swapping people playing alone or with faction banner first. This could be abused to fill a whole team using the same banner of course but just make an abooze rule and
BAN.
That way people playing together while on voice comm, possibly practicing, wouldn't be split up, because it's really demoralizing for team-play, especially when the person actually leading is suddenly swapped.
Obviously all the banner stuff could (and most likely would) rise a few new issues, such as people freely using whatever banner they want, it could fubar the balance sometimes, but hard to speculate about without seeing it in beta action shortly.