I'm not sure how wild this is gonna sound... but what if the Al-bum name is "Album 14", "Untitled", or is actually untitled? I've been pondering on this for a bit, & came up with a few reasons why I think there is a chance it could be.
Al was probably joking in this tweet, but that's when I started thinking.
"Okay, so apparently there may be some “legal issues” with calling my next album “Led Zeppelin IV.” FINE, I’ll think of something else."
Led Zeppelin IV, is essentially an untitled album (no titled was printed on the cover) & that's it's nickname (one of them it is well known by, though there are others).
If Al were to keep his album untitled & tried nicknaming it Led Zeppelin VI there would be legal issues
That's the joke from Al, but it can maybe be considered some kinda subtle hint to being untitled.
Remember the white after Labor Day tweet? Al looked like he was on some kinda black backdrop. What better than to have him & the band in all white on a black backdrop for the untitled album cover? Plus to me, it looks like maybe it was taken sometime before Labor Day... possibly the album shoot?
Also the first studio album was self-titled, don't you think it'd be some kinda clever thing for Al to do by having the possible last studio album untitled or naming it "Untitled" ironically?
This is just a theory of mine & I could just be over thinking everything, but it is some food for thought.