You brought up at (I didn’t want to answer there/derail the main topic?):
It could be argued those packages would depend on 1.x+1 but that wouldn’t solve the problem, because then yes those versions would no longer be installable in that Julia, and would force use of older versions of the packages, that also wouldn’t work.
So it got me thinking, should it be the other way around, Julia having [compat] on some packages? I’m just not aware that Julia has a Package.toml file per se (at least not the compiler), only some stdlibs of it.
These are very much special cases, and I believe core devs may be involved anyway, and this would require a new version tagged to work with a (an otherwise) breaking Julia master, that’s about to go stable.
In theory any package can depend on internals of Julia and break this way. And I’m not proposing a long list of all those. But your argument is that there are only few (plus its indirect many dependants). Would this be a good solution, would automatically fix the dependants, and most of the ecosystem?