In general the idea wouldn't really work due to the mana-management side of Arcane; but as Imnick suggested a proc from a Tier set bonus would be nice, esp. during Alter Time or something like that XD.
First suggestion straight out no; Arcane would then basically become a 5th paladin spec (4th being current Shadow w/ Orbs and DP), and personally that completely ruined Shadow for me. I don't mind the idea of having to build a resource and then consuming it, but Blizzard needs to try and keep uniqueness among classes as it'll just get boring after a while. Could argue that Arcane already has resource management built into the playstyle anyway.
Second suggestion is decent, would possibly promote a playstyle away from trying to camp at 6 stacks as long as possible; especially if it only affects casting speed, instead of Haste (would become easier to balance due to not factoring in mana regen).
If Blizzard changed Barrage to be more rewarding to cast so dropping stacks wasn't as punishing (something similar to Fenixx's casting speed (not haste) suggestion or perhaps buffing the damage slightly, it would probably be added to the rotation. Instead, they just give us another way to 6-stack camp which apparently isn't what they even want us doing, so it's not really Barrage that's broken.
6 stack camping wasn't intended and therefore is broken just by the concept. Also, Blasting at 90% mana isn't failing depending on what CDs you have up. Difference between using Ice Lance and Scorch is that Ice Lance will be nothing more than a GCD to use, Scorch is (more often than not) above the GCD and allows more regen time. Considering we'll VERY likely switch to Haste/Invo build come 5.2 6 stack camping will come from Evocation not having a cooldown, not from Ice Lance spam. Ice Lance also hits very little compared to Scorch even with Arcane's Mastery.