Proposal 1 for making opam switch create <version> avoid ocaml-system coherently with the new behaviour of opam init introduced in #6307
Mentioned in #6407 (comment)
Proposal 2: #6466

Pros:

• The set of default compiler packages is now arbitrary configurable via opam option

Cons:

• if someone relied on the previous behaviour using arbitrary package names, it is now hard to do
• this makes opam a bit more opam-repository specific by default, without changing the new default-compiler option