Honestly all this fretting and hand-wringing over a plug! My plug is better than your plug....! Don't switch to X plug or my car will be rendered worthless, boo-hoo.... (Don't worry, it will be worthless because of battery degredation, not a plug....)
When electricity was introduced, original wall outlets looked like light sockets (female) and plugs (male) on lamps and appliances were screwed in like lightbulbs. The U.S. two-pronged, flat blade outlet standard was eventually introduced as the standard. Then, much later, the three pronged grounded outlet standard was introduced. Homes were adapted with time.
Things evolve, things adjust, and improve. This is ground-floor EV tech here. Everyone should be smart enough to know that things will change, and likely rapidly so. We survived the switch to Unleaded gas without catastrophe (remember that...), we can survive a potential change in a plug....
If Nissan thinks it is best to adapt to the SAE plug, who cares! So what! It's a plug! Or, vice versa if they stay with Chademo while everyone else goes with SAE, well OK too.
There will be adaptors developed or L3s will have both style plugs, at least for the near future. I think companies are smart enough to get there are a lot more Chademo EVs out there, for now, than SAEs. Nissan will not leave thousands of Leaf owners stranded without a fix, I'm sure (I hope). They would ruin their whole EV project if they did.
The fear old Leafs' will be left in the dust with a plug as obsolete as a parallel printer port on a computer is simply speculating, making a mountain over a mole hill. Whatever happens, I have some faith that Nissan will not leave current Leaf owners without help. If Tesla can devise adaptors for its plugs, then I assume Nissan has the brains to develop a Chademo to SAE adaptor as well.
I hope.