The actual blend modes have problems with alpha and other performance issues.
This task is for do a full review and improve and fix these issues.
We move it to 2.81 because for 2.80 is too risky to change draw engine, and it's better to have something running with some problems that breaks the draw engine.
I initially assign to @Clément Foucault (fclem), because he will coordinate the task.
Examples of the problem: