Add this command to some feature. Maybe it is intention that you have to put it down take what out and put it back pick it up etc but it is such a pointless waste of time.
With this notion, you are just suggesting to have a command to bring up a secondary inventory window at any given time. Even if something like this were to be implemented, I don't think it would be implemented with enderchests, but more so just an alternate inventory window. I personally feel that we have enough inventory space as it is, and it doesn't take too long to drop off your inventory at home, then go back to mining.
Just carry a few enderchests when you go mining. Boom! extra inventory at your disposal. Just make sure to bring a silk touch pick and your all set. Edit: Also i wouldn't trust a command over a actual chest. So i'd rather take the time and place down an enderchest.
Lol, that is what I do (and what i am complaining about having to do). You can say there is no need for something about almost anything tbh; for example we have /wb and I don't hear anyone complaining that this is unnecessary and that we don't need it. Sure, I could carry one and put it down every time (I did do until I got /wb) or nip home to use one etc etc. Still just seems like makework, maybe I am just lazy .-)