very unlikely. Namespaces is major change which is impossible to
backport to 3.x without violating semver.
Theoretically you can use namespaces in ss3 already, so theoretically
you could create a namespaced module that works both in ss3 and ss4.
But, it has tons of issues such as template names and if you want to
support both ss versions you need to create class aliases for classes
that are namespaced in 4 but not in 3.
In the end you will end up with more work than maintaining 2 different
versions unfortunately.
(I attempted to use namespaces in mysite for a couple of projects with
ss3 and had to stop doing it because it just introduced to many issues
and needed to many workarounds)