3.2.0 is the next version that is being developed right now. That means there will be no 3.1.4. It is not a big deal as we keep backward compatibility between minor releases (in this case, between 3.1 and 3.2). That means you can use libraries compiled with 3.1 (or even 3.0) as your dependencies in the 3.2 project. Regarding source compatibility, updating from 3.1 to 3.2 will be as easy as updating from 3.1.1 to 3.1.2.
We are no longer in Scala 2 world, where 2.12 and 2.13 were different compilation targets and needed cross-compilation.
There is still, of course, the problem of forward compatibility, which may be important for projects that are unable to update for some specific reasons. We plan to address that by the LTS version (currently scheduled for 3.3). The blog post announcing this is now under public review.