So turns out I simply forgot to connect the AUX_GND pin for the DisplayPort connector, a quick bodge wire and DisplayPort was working as well :)
Ethernet is only 100Mbits because I mixed up the connector pinout. Molex had two versions for the part that I used and for some reason the bi-color MagJack has a different pinout for the diff. pairs rendering 2 pairs useless which makes me end up with just a 100Mbit connection.
I have ordered the correct part for the pinout and will see if it works ok after reworking it.
I'm currently in the process of designing the next prototype which will be the actual first prototype meant for the tablet instead of a SBC like before.
It will be as compact as possible and breakout everything over FFC like I planed. This also means I have to spec the electrical standards for each peripheral. This will probably not be final but its important to keep future solutions in mind here already. After all its supposed to be a universal standard for portables, not just for my initial tablet here.
I expect this to take another 2-3 weeks as I wont have too much time due to private life stuff.
But I want to see it assembled in mid July and maybe do a second revision before the judging deadline in late August.