Gunner would be super easy to do as Bastion is already basically gunner already, you just have to have the chaingun ability turned on while walking and hand it to a chick hero.
Already has a sniper w/ Widow and yes she already has a grappling hook.
Already has an engy, however with the new update on Torbjorn you could make the sentry up-gradable again.
Sombra already can go invisible, so spy wouldn't be too hard.
DVA bomb = Cyborg ability.
Soldier is easy enough. Same with Scout type hero.
So yeah, totally doable with a few lines of custom gameplay. Anybody try this workshop out yet?