It's probably not a problem, nice thing is that the existing kernel sources will stay available, so even if special systems need to run on 486, they can always build kernels.
There's probably no intersection where 486 legacy systems are going to be in need of kernel features that are not already implemented.
In that unlikely event, it may still be possible to backport said feature to the last 486 compatible kernel.
Comments
It's probably not a problem, nice thing is that the existing kernel sources will stay available, so even if special systems need to run on 486, they can always build kernels.
There's probably no intersection where 486 legacy systems are going to be in need of kernel features that are not already implemented.
In that unlikely event, it may still be possible to backport said feature to the last 486 compatible kernel.