It's not proposed though is it? It's actually happening. A proposal infers that there has been an inclusive discussion where a consensus has been agreed.
I have just heard about this and it's a like it or lump it edict, not really a proposal.
It’s a trial. FIFA runs dozens of trials at a time. The blue card is just one of several trials around Sin bins/cards that’s being announced at the same time.
It will be used in some random youth league like the “daylight offside” trial going on in Italy’s u21 league at the moment.