Awesome post! Here is how I see Dominion roles:
Someone who can interrupt from a safe distance or travel extremely fast.
Cassiopeia, Sona, Ezreal, Gangplank, Pantheon, Maokai, Xerath, Kog'maw, Heimerdinger
He may not have miles-away poke, but that's because he can defend a point forever. Often has crowd control that can hold the enemy under point fire longer.
Nunu, Galio, Rammus, Maokai, Singed
The brawler can stray from points a bit. He chases enemies off the point while his friends cap; or he runs around the inside of the map to stop enemies from traveling safely. Some supports who do not fit other roles can be most helpful tagging along with a fighter brawler.
Jax, Akali, Tryndamere, Olaf
Karma, Alistar, Soraka, Shen
Can backdoor, scout the map, "ward," or interrupt-outta-nowhere.
Teemo, Twitch, Shaco, Rammus, Pantheon, Twisted Fate, Shen (with another runner)
Kills minions so fast he can use them to yoink your spawn points fast. Popular in bottom lane, but if protected, he can snowball to cap enemy mid after a successful top lane. Just know when to retreat.
Singed, Heimerdinger, Sivir