It's not possible to have multiple 1.x.y versions of the same crate in your project, so you would need a really old library that depends on Tokio 0.2.x for that

It's not possible to have multiple 1.x.y versions of the same crate in your project, so you would need a really old library that depends on Tokio 0.2.x for that to happen. This isn't something that normally comes up in practice.