• specific version compiler (SVC) is required DUB-package itself, as named, with own version.
• project depends from SVC that is explicitly required field (maybe with constraint like 2.79<= AND <2.92).
• contra: SVC of total project depends from some unifying SVC of dependend packages that can differ from each other - that is impossible task.
  workaround: each package compiles by own SVC and the "last linker" links OBJs/LIBs it to EXE.
  must: packages/classes/functions/entites compatible at ABI level - same name mangling etc.

bonus: DUB will become indivisible part of compiler tools.

PS
dotnet became. nobody uses CSC.exe now.