Swift Mailer to Symfony Mailer - Will Swift Mailer continue to work?

I looked into Symfony Mailer for an existing project, but it is not a drop-in replacement like is advertised on the project page. It works in a completely different way.

• Swift Mailer is a simple implementation of a standard mail handler. It has a handful of classes and is stable and battle tested.
• Symfony Mailer does a massive overhaul of how mail works in Drupal. It has a huge number classes and introduces a whole new ecosystem of plugins and mail processors. There is no stable release.

It's probably great for new projects, but on existing projects it can be difficult to upgrade, especially when a project has a large number of mails handled in custom code and covered by unit tests. We ended up writing our own custom mail handler instead.

I wonder if it would be a good idea to turn Swift Mailer into a sort of Symfony Mailer Light, and create a 3.x branch that swaps out the Swift Mailer library with Symfony Mailer, while retaining the rest of the code base largely identical?

There is now Symfony Mailer Lite → .