I'm implementingflag FLAG_ROTATE for tilesets and sprites, that allows rotating 90º the selected item. This flag is implemented in Tiled editor and allow to rotate the brush in steps of 90º. Tilengine read and stored this flag for compatibility but ignored it when rendering.

Here is a preview of this flag being used to correctly render rotated brushes, combined with existing flags for horizontal and vertical mirroring.

I'm still having some issues when rotated sprites clip on the screen edges, but otherwise tiled layers and non-clipped sprites work well: