I would love to know if the longer slide/barrel of the full-size gun will fit/function on the compact frame. I've really enjoyed the possibilities of doing this with the P10-pattern guns, but to my knowledge the old P09 slide wouldn't function properly on the old P07 frame. I tried it years ago but I think the longer slide retracted too far into the compact frame, or something; it's been too long.
If they made the slides interchangeable this time I am definitely going to be picking up some new stuff...