As long as you are not blowing out your SM2.0 shaders with more than 64 math instructions, you are fine. However, I'm not sure how long Unity itself will keep supporting SM2. To be able to run NGSS on SM2 hardware, you really need very simple mobile shaders. If I'm not mistaken, I think Unity still don't support spot/point shadows on Mobile (only directional). This only applies for directional lights and custom mobile renderer that does spot/point shadows and want to integrate NGSS on them. PS: SM3.0 will remain for a moment (Desktop and Mobile) so no problem on that.