X-Men #19 has the kids out socialising when they just happen to bump in to a person with power mimicry powers (our first meta-power), who after tracking them back to the school, kidnaps Jean. The series could easily pass this off as a coincidence, but instead it reveals that he had tracked them intentionally. Mimic is frustrated by the nature of his power-copying - which is proximity-related - and plans to use a machine to permanently fix the X-Men's powers to himself. Turns out the machine does no such thing - it was constructed by his father to remove powers, without Mimic's knowledge or consent. After events run their course, Xavier gives him a windwipe and sends him on his merry way.
We have here the idea of a mutant "cure" touched on for the first time, although Mimic is explicitly not a mutant - he's given a science-experiment backstory, and everything. This is perhaps in order to sidestep the issue of whether or not the X-Men who have expressed a desire to become "normal" could use it, too.