my upcoming gravel bike will have 650b wheels with 47mm tires. I am currently running 700x38 on my gravel bike and those will fit the new bike. I wanted to make it fit 700x60, but decided that requires too much design work on the back end. Hopefully people will still make tires and rims for it, I think it's a good size. There are tons of new hybrids coming out with 650b tires, so I don't think the size is going anywhere.