Yeah, it's interesting that the devs abandoned that idea. I like the concept of having different abilities available to followers of different patrons.
The Primeval Thule Player's Companion has an alternate 14th level class features for GOO warlocks, based upon their chosen patron. For example, a warlock who has Nyarlathotep as their patron can turn into a swarm, a warlock who has Hastur as their patron can speak maddening gibberish, and a warlock who has Shub-Niggurath as a patron can change shape into an animal.
These variations add an interesting dimension to the class, and I've found them to have a substantial effect on the way players play the class, even though I've never had a campaign get anywhere near 14th level.