OK. Time for a committed player's point of view and so it is that I shall wade into the fray.
I am neither artist nor coder.
I am a player who likes to assemble whimsical scenarios such as using all 90 available in-game industry slots and then making decisions as to which survives during the game.
I like to use all forms of transport ... rail, road, air and sea, often combining them to move a shipment from point A to point B.
TTDX in its default form was somewhat basic to my wants and desires. Along came the Patch and a whole new world opened up ... features, features and still more features! A TTDX addict's dream come true.
Next came the graphics. Then new industries. My grf folder has grown exponentially.
In true addict fashion, I want more. HAH! I WANT IT ALL!
And so we come to ECS. I watched as it was developed, contributing an occasional suggestion, critique or round of applause. I was intrigued by George's implementation with plug-ins (vectors), making for a truly customizable gaming experience. Others saw the benefits of new industries, and so Pikkabird offered his most excellent UKRSI. And this brings me to my next point.
UKRSI is not vectorized with plug-ins. I wish it were. I'd dearly love to be able to combine some of its features with others from elsewhere. That gravel pit really rocks. (no pun intended ... well perhaps just a little.

). Instead, I believe, and I may be mistaken in this, that UKRSI was designed by Pikka as a typical British industry set to compliment Pikka's UK rail set. There was no thought nor intent of its being used with anything else. Thankfully, it does work with some other transportation sets. I believe that WhiteHand is following this same path with his NSW set.
So, rather than those two sets being generic "all things to all men" sets, they speciallize in presenting transportation as it evolved in some very specific geographic regions. Obviously making them fully compatible with other sets, whether via ECS or otherwise, is not primary to their design, however, for a TTDX addict such as myself, it would be nice.
I think that is the direction that Michael Blunk is taking with his fine sets, which I find to be quite adaptable.
Conclusion: ECS is a standard fully described in the wiki. It is merely a framework for people to build upon. Hopefully, for compatibility's sake, they will remain true to the standard, but if they should chose to stray a bit, that is ok too, even though it would limit the player's choices and experience.