The RK3588 for me is very client based (HMI, Desktop or Media) rather than server as why embed so much in the GPU unless your going to use it for AI with ArmNN.
Both look really interesting and for me the loss of the PCIe 3.0 is no biggie as the RK3568 is a monster SoC to previous but still is an odd match with a high performance 4x PCIe NVME and there is eMMC 5.1.
I have a question though as the Rockchip datasheet states PCIe 3.0 x2 2 Lanes which has confused me that why not state 4 lanes or is this merely it can be PCIex2 x2 or PCIe x4
I suppose you don’t have a ballpark figure for how much cheaper the Rock Pi 5a will be and form factor you might be considering purely as a possibility.