I am pretty sure Midi was adopted by all manufactures straight away, and was incorporated into all newly released products, (I think Yamaha started with the HX1 in about 1985. (The rest of the instruments followed as they were released)
Standards have to be universal, or they get limited use. (The big 3 on their own are the last ones you want set up a standard)
As to sending out codes for variations etc, then most instruments have had this capability for the last 10 – 15 years, but as there was no standard they were mot implemented by a lot of manufactures. (You aren’t going to get any sales unless your instrument can talk to other manufactures)
Whether you like it or not the MMA is the only way to go. (Not much point in starting something new when you already have good solid foundations to build on)

Bill