Ok, didn't know that, sorry!Lol. Project Butter is part of the Jellybean framework. Only custom roms on older devices using hacked together drivers can have JB and no butter. As MIUI is either based on stock Roms or IS the stock Rom, it always will have native JB drivers for the JB versions.
The already answered but anyway I'll explain a little more. The Qualcomm 8000 that's inside the Mi-1 is a completely different architecture than the Qualcomm Snapdragon S4 Pro inside the Mi-2. I had read some articles saying that some testing Mi-1's were spot with Jelly Bean, but there's nothing official so far.when you said that we need to wait for Qualcomm JB drivers for the M1 S
it is for the Dual Core qualcomm only , we can use the drivers from the M2 quad core version
Miui China did tell that the JB rom will be available ?