What would they get out of it? Nothing but an interesting story to tell, no doubt (the Japanese and Chinese response if they ever hear the story is obvious--"oh, more barbarians in the north, imagine that"). There's probably a reason they didn't get past southern Kamchatka, and that's because the natives there were easily a match for them. Sure, Komandorski Islands are uninhabited, but after there is very large and settled communities of Aleuts which I doubt our Komandorski Islands Ainu can displace.
Or could they? Didn't the Ainu have agriculture? Would their agriculture even work in the Aleutians? If it can't, then there's no way they could do that.