I currently run 5 PvE builds on my necromancer (PReaper, CondiScourge, AlacScourge, Healscourge, QHarb) and 2 WvW builds (Reaper, HScourge) and some random open world build.
Id love to add roaming builds or cele scourge for WvW or even a PvP build but I'm limited to the 8 slots.
You'd just make more money via gems and players like me would be able to use more fun builds to play with.
Also shouldn't be much effort on the programming side to implement this.
It's a win win win
I'd either increase the limit to 16 or just get rid of it alltogheter