Google's, sure. Some vendors make it painful (and in some cases, even impossible) to compile kernels for their devices.
Google is legally obligated to release kernels for their device. With Fuchsia, neither it nor any of the other hardware makers would be. Google might still continue to release their kernels — say, for developer contributions — but other vendors are quite likely to not do so.
Vendors won't modify fuchsia or its microkernel (magenta). That's the point behind the driver APIs in fuchsia. This should allow Google to update the full system, kernel included, while leaving the vendor drivers, which run in user mode and will still work due to the API being still supported, alone.
If Android is ported to fuchsia, that would solve the android update problem for good.