Easy-To-Understand Performance-Boosters.
-- Grouping (Baking) Objects together before rendering. Combining maybe a lot of (e.g. 100) Objects with only 44 Polygones to one Object. If they are not moving and static, that could be good for lower spec hardware. FireTV Stick, OUYA, etc.
-- Animation support functions for Spine Pro (Brashmonkey), Spriter Pro (Esoteric Software), Creature Pro (kestrelmoon), features like Mesh-Deforming. Skin-Swapping, Attach 2D Sprite to Skeleton, change texture Atlas, Inheritate Skeletons / create Instances with other Frame of animation
-- Auto-Texture Compression in RAM like Crabby (if not supported on every device or to complicated, it would be also great, to have ASTC)
-- Easy Export to Raspberry Pi (Linux-Image), Raspberry Pi Executable from Windows
-- better Raspberry Pi support, totorials, etc.
-- Convert Tier 1 to Tier 2
-- like Carharttguy said ... more export options. Xbox, PS4, Switch ... you don't have to have all, that are supported on Unity, but some more would be very great, or at least, a tutorial, how to archive export with HTML5 --> to UWP, and to other, like you have done with UWP in some way. (Maybe some automatisation there)