Spell hit seems pretty dismal still, and with no way of increasing it I've found trying out caster dps on the 60 dummy to be quite frustrating. If you want to go for it I would encourage it but you might not enjoy it, it's super frustrating to miss like 8 or 9 out of every 10 spells. Historically we've had DOT based casters do better, I remember an affliction lock for example on the EU project way back when you could gear for hit that did acceptable dps. DOTs in general have always done well for dps, I have some vague ideas why but not super sure. I would especially steer away from anything that needs you to land multiple spells in a row or stack something up like a fire mage, often you'll miss a bunch of your abilities building up to your big damage, and even if you do manage to get all your stacks and procs its more than likely that you'll miss the ability you've been building up to.
That being said though we've been surprised in the past and there's so much room for experimentation. I remember times when shadow priests and melee mistweaver monks were our top dps specs. Demo locks in the past have been viable since they do a lot of damage through the melee felguard. That's what I find so fun about this kind of twinking, you have to think so creatively and work so outside of how your class is supposed to function to make things work. With the way arcane missiles works right now, i.e. doing so much damage and being a spammable channel like mind flay, I could see an arcane mage doing decent just spamming arcane missiles at the target until one lands. Not a very entertaining playstyle imo but it would be worth a look. Just try stuff out and you'll figure out what works. Keep in mind though that you will land slightly more spells and abilities on the 60 dummy than you will with the raid content