my workaround which worked pretty well for the last few days does not work anymore. something (unrelated) might have been changed at plex.tv and i am still investigating. maybe this is a fault of mine, of which i am not aware yet.
this is a drawback, but i am in contact with someone who probably knows more about this than anybody else
I still hope we can find a suitable solution for everyone!
so i worked it out, seemed like my fault - lack of sleep is not a good thing while developing
i can confirm, that remote-play (not only local lan) is also working right now. the next step is to build a solution that will enable everyone to run their own reverse proxy with ease.