What is a "reference" system?

The ideal "reference" system would be that which is the most heard by the most recording engineers/people so that most everyone would have a common ground on which to base their opinions (i.e., a point of reference).

This is why I had previously alluded to the LS3/5As because most all British music is mixed, or at least sampled, over this set-up and most engineers would be familiar with the sound.

An American "reference" system would then include the likes of Altec 604s/JBL 4333s, at least for 60s/70s/80s music.

While not current state of the art, these were purchased from a recording studio and even at >45 years old this would qualify as a reference system.

https://youtu.be/iGa9259pz-I

 A reference system is defined by two factors:

 A--- The sound of  live acoustic instruments or voices experimented by each one of us in our life...

 B----Then the way the system room is acoustically designed for ONE listener to translate the recording in the best acoustic experience...

Great hall acoustics  dont use the principle and concepts  of acoustics for all listeners ears sitting in different position  in the same way a dedicated room did for the owner ears in one specific location...

Same acoustics science very different application...

There exist as many reference system as there is pair of ears...

A reference system is not about money and only gear pieces but about their acoustical embeddings...

the fact that some piece of gear are "reference" does not define a reference TOP system...

Well, I know you said you didn't want to open it up regarding YouTuber reviewers, but Hans Beekhuyzen has three "reference" systems. In his world, "reference" means three price points such that all components in each system are matched to each other in price.  In other words, he doesn't put a $10K DAC on a $1K integrated amp and $500 speakers. And yes, at each of these three price levels he switches review pieces in and out and lets you know what he hears and which system they are most likely a good fit (or not). 

There is no such thing as a reference system, when you don’t know the ins and outs of the recordings you have in hand.

Live music from the same band even is what it is...but, you weren’t sitting with the band in the studio or know anything about what all happened with the mastering apparatus.

My reference is live music, not a system.

My system IS my reference, the one that is most familiar to me.
I hear and know it's abilities and it's weaknesses.
I'm busy tweaking my diy's, so it's one ongoing project is to improve what 'it' is 'hearing' and do some r/t analysis on some screens.

...but the fun part is getting to play anything I want from a planet of choices.... ;)