Yes, the rockpi4a (!) is equipped with eMMC, but my experience was that uSD takes precendence over eMMC - at least on my board.
The eMMC has the working 4.4 debian kernel from radxa, everything working with the disks except for see above (idling disks crashes system).
When i ALSO insert a uSD an power cycle, the rockpi4a will boot from the uSD first, for example with the working armbian 4.4 image from radxa server (my first URL).
Of course, there may be more complications in the bootstrap process that i don't understand, but removing eMMC is really not an option anymore on this board, its inside the raid case with heatsink and M.2 adapter. It's already terrible difficult to squeeze the uSD into its slot because thats now hidden behind the PCI extension cable. Waiting for an uSD extension cable/board *sigh*.
Would be lovely to have a way to boot the board remotely, e.g.: without plugging/rewriting modules. Any netboot option ?