It is not a given that you will have problems with an implant when you have a metal allergy. No direct cause and effect has been proven in any studies.
But....when you do have a known allergy or sensitivity, you might have a greater tendency for problems with the metal ions (small microscopic particles) that can be released with the friction of movement in an implant.
There isn't a lot of information out there on this theory, but it's something I've seen a few documents on lately. The thought is that if an implant is placed even slightly out of alignment (so slight it might not even show up in a x-ray), it can result in greater numbers than normal of these metal ions being released. They irritate the tissue. You get pain, swelling and inflammation. And that causes a process called osteolysis where the bone dies back enough to start the loosening process. I am not suggesting this is what happened to you. But it is a theory that's out there. There just needs to be more research done in this area.
So please don't try to second guess what may or may not have happened with this knee. I'm glad to hear your previous surgeon validated what we said here about not going with any implant that exposes you to nickel. The important thing now is to get you to a surgeon who understands your problem and can give you the best chance for success after so many failed revisions. You most certainly don't need another failure.
Good for you for taking quick action here. There is nothing wrong with meeting with the surgeon you have surgery scheduled with on Wednesday so you can ask him some of these questions we've suggested, unless you've totally ruled him out. But, please don't rush into the surgery with anyone until you are confident that you're making the right choice for both your implant and the doctor performing the surgery.
Please let us know how things progress.