Should a reference speaker be neutral, or just great sounding?

A reference is anything you refer to. For words we can refer to a dictionary. You could look it up and see, that is literally the meaning of reference. Nothing about neutrality, objectivity, or anything like that. Your reference could be a Picasso painting of a woman with three boobs and a few other odd body parts. Your reference could be last years iPhone. 

A reference is nothing more than a standard. There's nothing objective about it, not at all. A meter is a reference, defined about as objectively and with as much precision as anything probably ever could be. Yet the meter itself is totally arbitrary. We just decided for convention to make it what it is. 

Same with your speaker reference. Totally arbitrary. Make it what you will.

Everyone’s “reference” will certainly be different. So many things determine the way we hear. The shape of your head. The size of your head. The shape of your ears. Even the size of your torso affects the way you hear.

Now let’s get into the room you listen in. And the list goes on and on. My reference and yours may be very different. With all these variables, what is neutral? Your neutral,may be tipped up to me. I think,of course,only my opinion,is reference would be what sounds great to your ears. A great topic with many different correct answers.  Now,if a speaker measures flat,do we all hear it the same way? 

One reference I can think of is Greenwich Mean Time.
What single loudspeaker model could aspire to the kind of acceptance that GMT has?
As others say, an individual can establish their own reference if they like, but it pertains only to them.
The rest is advert copywriter gobbledygook.  Along with SE, Signature, etc.