Should a hexblade be a subclass or an invocation tree?

Since we did not get an update for the hexblade it got me thinking we already have a good portion of its fantasy through pact of the blade invocation tree. Does it make more sense to have a whole subclass or to simply create more melee focused invocations?  

Armor/ shield proficiency via invocation?  Perhaps allowing to use cha in place of strength requirements?

Given the expanded scope for invocations in the 5.5 ruleset, I'm actually pretty inclined to prefer an invocation tree approach rather than the current subclass format.

On a related note regarding lore and class design: even with the updates, I still don't quite understand what the patron of a hexblade warlock actually is. The concept of a sentient weapon feels vague compared to the flavor of other patrons. Also, couldn't a sentient weapon just be covered by an existing patron category (like an object possessed by a fiend or GOO)?