This is the real problem with standards...
The other problem is the NMRA did virtually nothing on the connectors standard for many, many years, and I doubt they had any interaction with the NEM who seem to be much more on the ball about these things. That led to what we have today, People wanted more outputs, the NMRA sat on their hands so the manufacturers responded to the market, first 9 pins (US) then importing what was being done in Europe.
It's a brave move by Walthers to put the Next18 plug in their upcoming SW7. While I can understand the smaller size of the decoder would be attractive for a small model I believe they're locking everyone into a single supplier (I think only ESU makes Next18 stuff currently) which the DCC crowd seems to quite loudly disprove of and they're locking everyone into 4 outputs.
As for your wish, 9 pin is dead; it's gone the same way as 8 pin. 21 pin is what is now and hopefully everyone can see the forest for the trees and can get on board with PLuX; or we invent something even better
- Tim