Rastus, 2 big things if barrel and bolt could be made, the cartridge length is 1.137" for the 5.7 and only .590" for the .22 lr, and even the 22 mag is only 1.052" long, where would you get magazines. The diameter is much bigger as well. Maybe an M1 carbine, but they are worth too much now. You can get a 5.7 upper for an AR15, that takes the FN 50 round mags, but last I looked 6-700 bucks.
That upper is really cool, but I've got the PS-90 and don't want to remove the uppers I have from the lowers I have...of course that would be a reason to hook up with a new lower. ...maybe get that Tactical Solution upper too and swap from upper to upper... But, anyway, I'd prefer something that didn'thave the gas blowback system, etc.. for whatever reason. Maybe it's just the with all the hullabaloo for EBR's I am EBR'd out...I did pick up a Ruger Hawkeye the other day.
And yes...it's a tad longer...but ought to not take much changing in to go to 5.7. A minor change to machine the chamber of the barrel...the bolt is a block of metal, just machine the firing pin in center, change a couple of springs...voila'. Now..that extra 1/10 inch on the mag...I dunno if that would require a change in the receiver machining or not...I was supposing not but I could be wrong,
If Tactical Solutions would spring a conversion kit for a 10/22 I'd snap it up but there would have to be enough interest from the public to get Tacsol or Ruger interested. It's just with handloads you could zip a 40 gr Vmax at 2,500 or so and be zero at 50 and zero at 100, plus or minus in a "conventional" package without gas blowback....the PS-90, being a bullpup, isn't my ideal for hunting.....