eg. change this:

runtime: org.gnome.Platform
runtime-version: "46"

to this:

runtimes:
  - org.gnome.Platform/46
  - org.gnome.Platform/45
  - org.freedesktop.Platform/20.08
  - org.kde.Platform/5.15

Many people complain about flatpaks taking up too much space. Allowing for more runtimes to be shared between apps would take up less space. However, this has been denied.

If I am an app developer and I know my app runs on several different runtimes, why shouldn’t I be able to specify all of those runtimes? Are there technical reasons why this is a bad idea?

EDIT: I mean a list of runtimes of which one must be installed, not a list of runtimes of which all must be installed.