At Quave, we are working on packages that we and our customers use to migrate them to Meteor 3.0, so at least essential packages are not blockers in our migration path.
The documentation is also updated with Meteor 3 (async) examples.
If you are using percolate:migrations the transition should be simple, and now you can use an async function in your migrations without any wrap async.
Important: we are focusing on Meteor 3 so we are not testing this package against Meteor 2, but for Meteor 3 it will be running on our apps in production soon (once this build issue is fixed). That said, we are not using anything specific to Meteor 3 so it should work on both.