I believe that attaching as in grappling systems such as Muay Thai, wrestling, and Judo is a logical extension of WC principles especially for larger fighters. I believe that WC is at its best when these techniques are employed.
However, I agree with your general premise that WC isn’t attached fighting. I don’t think that referring to WC as attached fighting really represents what the art is even with the narrowest definition. I also am uncomfortable with the notion that trapping has come to represent what WC is to a lot of laymen. To me, WC is an art of kicking and punching like any other upright art with a few tweaks that give it a unique flavor. (HumbeWCguy)
***EXACTLY. There is no such thing as a wing chun clinch, for example. Its just not in the system, whatever the lineage. And yes, the Muay Thai clinch, wrestling, and judo are (can easily) be logical extensions of the wing chun idea about close quarter hitting. And the tools are already there for a hybrid marriage, ie.- whats learned in chi sao.
I hate bridges…

Maybe it is too much left over from boxing and judo, but when I think striking I think taking the guy out before he has a chance to get attached and when I think attached I think throw and submit. (sanjuro/Paul)
***SEE the above response to HumbleWCguy, Paul. Some of what one learns in pummeling within wrestling/grappling is not that far away from some of what is learned in chi sao except that some close quarter striking (vertical fists/ palms, etc.) can be thrown inalong with elbow strikes (and of course Muay Thai uses elbows in close quarters also). As for knee shots from some sort of clinch mode, generally they can only be safely done when you’ve got some balance/structure control on the guy - otherwise you are open to be thrown/taken down.
So with that said, I can appreciate this other piece you wrote, Paul:
“I have used ‘clinch work’ to get out of the clinch to strike but strking in the clinch was always ‘secondary’ to throwing in the clinch.
When I did MT it was really hard to get into the ‘hit in the clinch mode’ because I kept going for the take down or throw, when my opponent would clinch and try I knee I would sweep or throw, I have to really drill the hitting in the clinch thing to get in the mind set of it when I started competing.”
…
***I THINK that YungChun/Jim put it well when he wrote this:
"Of course it depends on exactly what is meant by ‘attached’…Generally moves that lock up, prevent natural (economical) transition to continuous striking are outside the realm of VT…
Now, what the hell does ATTACHED mean? In VT there is precious little sustained sticking or attaching.. There are times when this could happen but then it’s because they are/were fighting for the line, interrupting our attack and then still each move only stays for a moment. Sustained energy issuing could result from hand replacement but even then it is a string of multiple short controls not a sustained attachment."