This doesn't follow for me. They can trivially allow it to still respond to the old wakeword. They should absolutely change the name in the event they can finally make it useful, because "Siri" is (in my mind and many others') a synonym for "hapless idiot." "Thanks, Siri" has been uttered hundreds of time in my house and my car, and 100% of the time it's sarcastic.
Many of those people will speak a language that’s not English, or live in the EU or China where it’ll still be “Siri”, not “Siri AI”.
“Do you have the new Siri?”
“Yeah I updated… but she still seems so dumb”
“Oh yeah… well that’s Siri for you I guess”
Horrifying for marketing folk, I would presume. You’re just setting people up to confirm that Siri is always useless and improvements are invisible.