For those commands to work, you probably need flatpak and ostree from
yakkety-proposed. It's still in -proposed because I haven't sat down
and verified https://launchpad.net/bugs/1656712 yet. I need to make
sure that the upgrade works correctly for those who already have
flatpak apps installed.
I have ostree and flatpak installed.
The usage of the old syntax (Installing a remote repo and installing an app) works for me.
I installed a 3.22 platform and a org.gnome.Games app.