...will drop support... There. FIFY.
It's not happened yet, and when it does, mainstream Linux distro's will remain supported in i386 for several years to come, because they will keep the older kernels in their LTS repositories for quite a while (Ubuntu will drop support first in 18.10)
I estimate that I'll have retired all my i386 boxes way before Ubuntu 18.04 drops out of support in 2022 or 2023.