I think you need to check obstruct between GPU power connector and frame, bending the riser may cause damage after long time using.
Design to use standard GPU is not good idea because it's not popular in market.
Thanks for the comments. The maximum gpu hight the casing can occupy is up to 128mm which a very common hight albiet a recessd power would be better in any circumstance. These numbers will be solidified after prototype testing.
As for the riser bend, any cable in general is prone to damage after long period of time. I have been using a riser that is bent and twisted for a couple of months and could not see any noticable damage. This is very dependent on the riser cable quality.