Anecdote, but Cash is just as popular as Venmo among my friends/acquaintances/colleagues(mid-late 20s, pacific northwest). Everyone has both installed because you never know who's going to prefer which one or just happen to open that one first.
Err... I'm old, but we have hip and trendy tourists?
Ah well... Another anecdote for ya.
Square, meanwhile, is offering both business and peer-to-peer options.
It might be a generational thing, but it does seem like Venmo has cornered the p2p market.
Yeah, I even have a landline. I did mention I'm old. ;-)
Worst case, you'll see people using online bill pay to mail eachother's banks checks as that is free and low effort. People just don't want to pay to move money friend to friend, and the US is an anomaly with our extremely high credit card processing charges, where we're at 1.5% to 2% in interchange, the rest of the world is below 1%.