Actually I had that exact idea, I am literally working on an ancient protectron companion named XY-17b who was made years before the war, worked as a security bot, repair bot, Enclave drone, and has met the Vault Dweller briefly from fallout 1. I plan on him having a lot of dialogue to learn about his past and being able to upgrade him similar to ED-E.
The reason he chooses the player is cause he knows the player is young, fit, dedicated to the cause, and tactically advanced when it comes to combat, so the player's chances of survival are greatly boosted over the other NPC's in the wastelands. He has been to New Vegas, New Reno, Vault City, and a bunch of other places, so when traveling throughout DC he is not going to be familiar with the surroundings since he hasn't been there long, but has been in the western area of the wasteland, so when in the New Vegas map he is going to recognize things and places.
The reason he is so different from other protectrons is cause he has been upgraded multiple times by RobCo and Big MT for use with the Enclave. I gave him a pretty robotic voice, doesn't sound human. Yet I am still working on the dialogue, if someone could help me with the model of him and the textures I would be greatful, since he has a lotta dialogue its gonna be awhile, plus the scripting for the events and stuff.