I'm not entirely sure Ian is running out of guns to cover, he's probably "optimizing " better his content output (after all, there's truly a shitton of guns around, and he has not covered a lot of stuff I've seen in museums around Europe, hell, he hasn't covered rare-ish pieces that are in my own collection). He's probably thinking long-term, the daily good video is a thing of the past.
It does make following the channel less interesting, though. Pieces of QA repurposed as videos, shilling (how to forget the embarrassing "buy a Scottish title") and meaningless stuff that doesn't strike me as particularly... noteworthy. I'd almost prefer if he started covering more actual use of some of his Forgotten Weapons (so, Forgotten History) or, god forbid, more on accessories (like his suppressor videos).
As some of you said, a good part of his audience is Euros or noguns that aren't particularly interested in the shilling. I wonder if this will cause some push-back.