The real 1911 frame + .22LR conversion is a better idea than it sounds. At first, I scoffed and bought a 22/45. Much later, I still can't fall in love with that thing- I wish a conversion kit would work on my 1911 (it has a ramped barrel, so none of that for me).
Really, though, if conversion kits don't count, there is no such thing as a .22LR handgun that is interchangeable with a larger caliber defensive one (well, except for maybe the S&W 617, but then we're talking revolvers). All of them will have minor variations from other guns, but no more so than you might find in terms of variance between, say, a CZ and a 1911. Either will require a bit of familiarization when swapping over. Ditto .22LR pistols.