Initial thoughts from me is I'd love to handle one and get a first hand view prior to buying. Unfortunately the only ones I've found are from Questar which is mail order only eliminating the chance of checking it out prior to purchase. Given, I assume one could go look at a normal P220/P226 etc etc... to get a feel for it. I've given a P220 in .22 a lot of thought as I'd like to upgrade to a .45 but would prefer a 1911 so if I bought it it would be strictly for 22. But its an awesome idea knowing you could practice with it cheaply using the 22 and then switch over to .45 vs training with the higher price of the .45 ammo. Magazines wise I'm not sure how cheap they can be found but through Questar again its $50-60+taxes per mag so it would add up real quick getting a few in .22 and .45. Accuracy wise obviously wont be as good as a target pistol with a longer barrel but I'd imagine it would still be pretty decent.
In the end, I was mostly on the fence due to availability of it all and the what if factor of it breaking or needing repair and having to deal with Sig out of country etc etc...
Edit, one thing I forgot to mention which I'm not sure about is the difference when going from .22 to .45 via the change kit. P220's in .45 are DA/SA. The Classic .22's are SAO. So if you got the Classic .22 then went to .45 would it still be SAO only or does the xchange kit some how change it over to DA/SA?