The future of CI

I think that CI4 will be one of the "modern" choices for developers looking to migrate from CI3 when they are ready to (for whatever reason).

Symfony 4 looks like direct competition, with a similar philosophy/strategy to CI4. They differ in that their components each have their own repo and would be individually composer-installed, whereas composer is an option with CI4, not a requirement.

Laravel will continue to be direct competition, with its own pluses and minuses.

I think the transition from CI3 to any of these will be "time consuming and difficult", but Killishan has put a huge effort into making it as painless as possible, and writing up some transition techniques in his blog and upcoming book.

CI4 has my vote, but then I might be a bit biased