Good example, this one helped me to understand the plugin function better.
I added the note about changing qmake to qmake-qt4. I found this on another page about making mythtv itself. Maybe I shouldn't have yet - I haven't been able to get everything to make, I need to update some other packages first.
Code change between 0.26 and 0.27
This commit made several changes to the plugin code
For HelloMyth, this means a line is changed and an additional include is needed.
I have Ubuntu 14.04 with Mythbuntu repositories for 0.27 setup. I had to do a git clone of the 0.27 branch with
git clone https://github.com/MythTV/mythtv.git -b fixes/0.27 --single-branch mythtv/
Ran the configure script with ./configure --prefix=/usr
Then did the build and install, the plugin works.