You could do that. Your quickened cantrip could be GFB or Booming blade as well for an additional attack. Sorcery points are the limiting factor on the quickens.
Either way, Haste is a great idea. As long as you have sorcery points you could make 4 attacks in a round (Attack, Extra attack, Haste Attack, quickened BB or GFB attack).
Hell, if you have Haste up and running for 3 attacks per round and you have Agonizing blast, you can then drop a quickened Eldritch Blast for essentially another 3 attacks in that same round.
If the target is subject to your Hex curse, you'd be dealing a potential metric ton of damage to a single target.
Mutliclass to fighter to pickup Action Surge and get another set of Extra attacks on the target as well.
In a full nova round you could get 5 attacks + 3 EB bolts each dealing Cha+Proficiency+damage dice to a target.
It's not the peak of melee potential, but it's good for sure. Burn another invocation on Eldritch Smite and then you can really maximize those spell slots and crits for damage when they roll around.