Haiku graphics driver API (accelerant) have 2D acceleration API (B_FILL_RECTANGLE, B_INVERT_RECTANGLE, B_SCREEN_TO_SCREEN_BLIT). app_server has code to use that, but it is disabled for long time. It was discussion that it is actually slower that current software drawing. Also if I understand correctly, it doesn’t support back buffer and will cause terrible flickering if enabled especially after disabling flickering workarounds (#15623, hand-made double buffering per-application).
Is it still needed or it can be dropped now? Can accelerated 2D drawing be used on back buffer and copy regions between buffers? If not, it is not useful anymore. Only hardware cursor and overlays may be still useful.
I think that acceleration should be focused on OpenGL based 3D acceleration because modern video card work in that way and it is more flexible (can operate on multiple buffers, alpha-blend and scaled blitting, shader-based gradients etc.).