It's not so bad really – having done it a few of times on fairly large code bases. Upgrading a project for a new Julia version is very straightforward: change the julia version, run your tests, and making any changes that warnings tell you to make. It's about as difficult as fixing compiler warnings in C – it's tedious but not hard.
Keep in mind that in the future this statement would be something like: if you have code that was written for Julia 1.x and want to upgrade to Julia 3.x, then you should upgrade through Julia 2 instead of just skipping it. This does not seem terribly unreasonable.
That's only if you haven't touched your code in 2 years or so, and is also just an issue with early adoption. There's a reason why Julia wasn't labelled v1.0 yet, but post-1.0 is where the syntax is stable.
Keep in mind that in the future this statement would be something like: if you have code that was written for Julia 1.x and want to upgrade to Julia 3.x, then you should upgrade through Julia 2 instead of just skipping it. This does not seem terribly unreasonable.