Hello Radim,
OpenPLi 6.0/1/2 is a good successor to OpenPLi 4.0, it is supporting properly the IPTV Protocols, and has improved a lot, and is very stable.
The online update is always a problem, due to the lack of space (more you put software into the image, less space is naturally available). This told, it's worth the step, upgrading to the newer images, that are much more comfortable and stable, as well as improved a lot for software.
You can also do the same swap of files/folders with OpenPLi 6.x versions, as you done for the previous version. It really depends of what you want to install on the image, as most of the software needed is already built-in now.
Old hardware, works very well on OpenPLi, an it's one of the best images as the box seems new and very speedy.
About Japhar, due to the lack of support of Ferrari, a small group of ex-Ferrari Forum members created the Japhar Sim. Then as you know estar, sim2 etc went dead as well, so it's the only team giving support today for the non-official hardware DM800HD/DM800HDse/DM800HDseV2/DM500HD/DM8000HD/DM900UHD/DM520HD. Japhar Team has it's own support forum that you can find with Google. So to use the Japhar images you will need to swap your old unsupported Sim by the new Japhar.
TS