There are issues that need to be sorted out that are quite substantial(right now it's overlapping all the gui elements for example). Even if it was fleshed out, Android is currently suffering the most from it, though Android has framerate issues all around. Graal really needs to lower the display resolution for high-dpi devices as it's rendering at 2560×1440 for my Nexus 6 even though it's visually unplayable zoomed out at 100% anyways.
And there needs to be actual substance to a day/night system other than just looking pretty.