Best estimates on 3.x LTS for new project work

As skunkbad said above, I also recall two years being mentioned by the CI team. I do not think there is a specific date.

But even if it does expire, there are still all sorts of possibilities, from fixing any issues yourself or a CI3 community continuing with a fork etc.

I would use CI3 quite happily and with confidence that it is a long term solution for your project.

Best wishes,

Paul