Not very long i guess based on the comments from Sundar/VP of communications at Google's comments. They say they have a great plan for user acquisition.
This is a new ground up video app and so the performance is better compared to other apps(I tested it, its definitely better than hangouts/messenger/skype, but probably same as facetime quality).
Haha! I understand the comment, but what i want to infer with that statement is that they are very serious about this app and not like other apps(Inbox/G-board/Spaces) which they launched and tested. Allo & Duo has been launched in the I/O and you can figure the importance from it.
And how far in the future will that be? Will Samsung install it on their phones?
I'm sure Duo isn't bad, but I'm not going to be able to convince my friends to sign up for it when Facebook Messenger already exists.