Lakka devs already have a bootable XU3 image that should be more or less copy/pasteable into our buildsystem to provide core board support. However Retroplayer != Kodi. If the device has DRM (direct rendering manager) support in the kernel (ideally mainline, worse some odroid specific kernel) it should be fairly simple to get the Kodi (Leia) GUI running as the DRM framework in Kodi is now quite mature and has been tested on a wide range of devices. However GUI != awesome performance and hardware decode will require an Exynos V4L2 driver. If that also exists things become theoretically possible but you'll hit some challenges with V4L2 support being on the bleeding edge of current kernel and Kodi development and some of the 'standards' are still in development and a little fluid right now. The main API that things need to coagulate around is targeted for the 4.19 kernel which is late summer, although things are now close enough to end spec that developers have something to pursue that won't need major rework when things are finalised.
While that's generally positive, the normal challenge with older boards (even great ones) is that by the time all the standards settle down a new one appears (with different chips) and then the number of technically capable people interested on adding support for the old model drops off because they all have new shiny playthings to poke.