The subject of disk space and flatpaks came up in the most recent
workstation meeting, and I'd like to separately discuss that in this
thread before creating a flatpak issue.

The full log:

https://meetbot.fedoraproject.org/teams/workstation/workstation.2019-10-28-13.00.log.html

Excerpts:

13:16:07 <langdon> allocating enough disk if you have your drive
sliced up is tough
13:16:36 <Son_Goku> and yeah, the disk space issue is a huge problem
...
13:16:47 <kalev> "the disk space issue" ?
13:16:58 <otaylor> Son_Goku: why would disk space be an issue?
flatpaks store data in $HOME
...
13:17:19 <langdon> that's the problem.. normally I have a "games disk"
13:17:27 <Son_Goku> likewise


Neither sysroot nor $HOME fits the above use case, where the user
wants to store games on a separate volume entirely. And another use
case is where it's desirable to use the much larger /home volume
storage pool, but permit sharing of apps among users.

Could there be a /home/share/flatpak with the appropriate permissions,
that meets both use case requirements?

Alternatively, Workstation could do what Silverblue does, with
/var/home bind mounted to /home - and therefore system and user
flatpaks go on the same volume. But there should also be a way to set
the default location for flatpak files. Users wanting a games volume
could bind mount it to /var/lib/flatpak, but then they need a way to
set system as the default location instead of users.