It will take about 10 years for it to become a viable standard.
No, the AV1 bitstream format will be frozen later this year, browsers will add support for AV1 soon after that (Mozilla, for example, is already working on it in Firefox), and YouTube, which is the world's largest video site, intends to start using AV1 as soon as possible. AV1 will be adopted quickly.
Considering how many devices out there that won't support it.
Many devices will be able to support it in software. My iPhone 7 doesn't "officially" support VP9 but VP9 video plays back just fine in VLC for iOS.
Nor will I be re-encoding my videos until forced
You don't have to re-encode anything unless you want to.