The theme is old and it has been exploited like a South African goldmine.
At the end of the day, all the outtakes from the different phases come from different sources. As I mentioned elsewhere, it would be interesting for me to know if the source that shared unfinished rehearsal room versions of Kit and IHTWTWYAS has any more material from 1997? (REYNOLDS TO THE RESCUE) According to Whyte, Morrissey just still felt like recording more after finishing Maladjusted, and so there were numerous more sessions in England during the summer of 1997. The planned Covers EP also falls around this time. Although Alain knows, that fans are on the lookout for such material, it is unclear whether there really is a Morrissey version of The Who's "Can't Explain", for example. More likely no. At least, that was their intention to do this as an interlude between proper recordings but Island/Mercury kicked them out.
Then again, at the duo concert with Alain, shortly after the Millennium, Boz plays Kit acoustically and says there's not much unreleased material, but that's one of the songs.
Allegedly, during the sessions with Langer/Winstanley in 1990, many recordings were also "left on the cutting room floor".
Even for an unfinished version of "Kill Uncle" there is a great desire somewhere.
Southpaw secrets have been given away nearly completely, IMHO.
Arsenal and Vauxhall must be thin on the ground too.
Viva Hate: maybe 1-2 more Street demos but they've managed to meet and talk about the reissue, so they won't appear any time soon. At least, we were offered 2 of those early demos.
Quarry has the "Home is a ?", as mentioned by @famouswhendead
, demo at least. But I'll bet there are rough studio versions of "Noise is the best revenge" and "I'm playing easy to get" too.
I think a Morrissey boxset with such recordings (similar to Springsteen's "Tracks") will never see the light of day during his lifetime. It's more likely, that Sam will give away more BOT demos as a "present" in 2023.