I agree that best place for “experimental” ISO should be cdimage.ubuntu.com. Of course if Canonical would allow this. This is traceable source that would somehow convince all people that Unity flavour has future.
If we talk about naming we can make it “simple” like other official flavours (ubuntu-mate, ubuntu-budgie) or we can be somehow “original” but at the same time not to distant.
Maybe something like “Reunity-remix”, “Ubuntu-reunity”.
But all previously mentioned proposals (Ubuntu-Unity, Uubuntu or Unitybuntu) are absoultely acceptable. Naming is not main goal at the moment.
Beside testing of unity-session under “parent” 18.04, parallel testing with early ISO is absolutely preferable. Let’s face it - at the end majority of people would like to have clean ISO with Unity only for fresh 18.04. installation.