No indicator of AI writing is going to last forever. We really shouldn't over index on the oldest indicator (which is liable to decay first). People are starting to say "delve" more in verbal conversations. This treadmill will keep moving. Unfortunately we have little choice but to keep up with it.
(Hint: No, he's not replying with AI. Two hyphens are not an em dash. Even then there's no hint of it being an AI response. Also the person is actually the CEO of Dropbox, the very person this thread is all about. You only have to click his username to see his posting history to see he's not an AI bot posting endlessly, his last posts (prior to today) were in 2024.)