When/why did Amtrak drop "Express" from Acela?
 

Was booking some trips today and noticed that the Acela Express is now branded just as Acela — e.g. https://www.amtrak.com/acela-train, and on my eTicket the train name is showing as just ACELA vs. ACELA EXPRESS on previous ones — any ideas when/why this switch happened? (Maybe to coincide with the Acela Nonstop? Or to acknowledge that the Acela really isn't all that express :p)

The change seemed to coincide with the Acela Nonstop rollout

Yep. If you look at dates after the rollout happens, you'll see "Acela" and "Acela Nonstop". My guess is that someone decided that "Acela Express" and "Acela Nonstop" would be a hair confusing.

Exactly, given that in most of the world an "express train" is basically what the Acela nonstop is, a "local train" is basically what the NE Regional is, and the regular Acela would be somewhere in the middle.

The proper name would be Limited, but that might be confusing.

And complicating matters further is that Acela uses different rolling stock than the NE Regional, and is basically a different product line despite serving (in many cases) the same endpoints.

Whereas, on a typical commuter rail (or subway) service, the only difference between the "express" train and the regular (i.e. "local") train is the number of stops it makes.

When Acela launched, there was also a period where (some of) the Northeast Regional trains were called Acela Regional, just to make things extra-confusing.

...and then there was the period where they referred to business class on the NE Regional as “Acela Business class”. Great branders they are not.

At one point, didn't Acela also have their own logo apart from Amtrak and even their own crew uniforms?