So the question of upgrading to Kdenlive 15.04 raises a question about a backout strategy. Considering the testing of 15.04 has been limited (by Vpinions own admission) I am wondering can you backout to 0.9.10 while running on a U/kubuntu 15.04 distro? IE can you run KDE Frameworks 4 on >15.04 distros ?

Since it is not in the repositories and I can find no PPA, I suspect the answer is no. You could try adding the Linux Mint repositories to Kubuntu which is doable, but can become messy if you aren't careful. I would test it out in a VM first. Mint will not make the switch to Plasma 5 until 2016.

Funnily enough when I created a Virtual Machine with Kbuntu 15.04 recently the version of kdenlive I got from the repositories that come standard installed version 0.9.10 of kdenlive with KDE Frameworks 4. So in answer to my own question - I do believe you can have frameworks 4 on 15.04 distros.

Yes, 15.04 and 15.08 come with qt4 support.

And as you've discovered, Kubuntu without the backports uses kdenlive-0.9 branch by default.

Other distros just need to be careful to use versions of mlt and frei0r-plugins that are compiled against qt4 otherwise you'll run into problems.

(Like in my case on openSUSE Tumbleweed I needed to use build.opensuse to build my own frei0r and then I can use libmlt and kdenlive from 13.2's packman repo - this was a pain, but worth it, 0.9.10 is rock-solid stable).

Maybe yet another backout strategy without the need for virtualization: the built script from the MLT toolkit site pulls a Kdenlive 0.9.10 if my memory serves me right. I've build it on a 15.04 system some time ago with KF5 installed.