I liked that point too, but when I went to use the text adventure bot, I found the delay immediately frustrating. It feels like I spend more time waiting for messages than reading or making decisions.
I too worked on a Messenger-based text game, and found that when you're sending sequential messages, the trick (though unnatural) is to add delays not based on the current message being "typed" by the code, but based on the previous message.
For example, if your previous message contains 100 words, and the current message to be sent contains only 10 words, you still want a long delay -- you're catering it to the user reading the long message. Similarly, if your previous message was short and the next one is long, the delay doesn't have to be long because otherwise you're just making the user wait for no reason.
That's super smart! Making the delay dependant on the reading speed instead of on the writing speed makes much more sense. Definitely adding this into my own bot.
This is a cool concept though!