Ive always wondered why wireless standards dont allow for duplex operation with say 2.4 one way and 5ghz the other? Wouldnt this help things?
It would, but only for links between two devices. In fact, this is how high end wireless backhaul links work. You have a low frequency and a high frequency and they're both used for duplex operation. But, that's only between two endpoints.
When you expand to multipoint wireless, your limitation becomes that an antenna can only send or receive, and only to one client at a time. So, because of that, multipoint wireless (with current tech) will never be a duplex medium.
MIMO makes it so that more clients can send and receive simultaneously, but you're still not going to have two antennas for every single client on your multipoint wireless network. Until we can figure out how to make an antenna send and receive at the same time, multipoint wireless will always be simplex.