"Casting will always be interuppted [sic] upon receiving direct damage."

[Zerosix]

Er....not only is there a PVP skill that gives you a guaranteed non-cancellable cast, now you have a use for [Surecast].

Thats two options. If someones attacking you, pop Surecast and cast sleep on them. If they cancel sleep use your other pvp skill and cast sleep on them AGAIN.

once they're down pull back and let the tank steal aggro.

The only people who will be bashing on tanks are bads who do not know how to pvp. The only way this would be viable is if tanks could force players to attack only them for a few seconds with taunt, or taunt would make enemies drop target.

[Noroi_Kisaragi]

The only people who will be bashing on tanks are bads who do not know how to pvp. The only way this would be viable is if tanks could force players to attack only them for a few seconds with taunt, or taunt would make enemies drop target.

Yes, tanks can force you to engage them. You can see it in the 2.1 trailer right here.
http://www.youtube.com/watch?v=R_aliYN8hNk&t=1m30s
Watch the chain. Additionally to that, provoke works in pvp as well (at least it did in the beta)

Casters will be just fine. Also I posted caster pvp abilities in a seperate thread if you wish to continue that discussion.