Hostage Rescue- not seeing much that's too difficult. If anything, there's gonna be loads of time to launch fireball, of all things- take out those mobs as people whittle'em down.
Convoy- yay for IS chains, here, even with resists- if you can kill at least one thing, the rest are gonna feel it. Thunder -could- be good too, if there's resists in that crowd? Fireball; too slow, but if you DID manage to get a couple mages launching it- pain will commence. Immense, horrible pain. But this last one is a massive if.
Scath- ohcrap. Not gonna be much time or room for casting- might want to just load up fusion bolts and Party Heal from behind.
I don't think mages are half as screwed as people say- I'm well in the camp of 'mages need a buff', but I can see chances to nuke and ways to be effective in the above vids.
Of course, we'll have to wait to play'em ourselves to really tell. Still, here's hoping for new mage stuffs... in G18 TwT
As for alchemists- I feel so much pity. So, so much. :<
One word for you.
[SPOILER="Spoiler"]LAG[/SPOILER]