Not really, no. For manufacturers it is faster to just write the drivers once for their chip, and release them targeting to an exact Linux kernel version rather than actually writing good enough code that it goes through the LKML process and gets merged into mainline. It costs money to update the drivers later on and it especially costs money to mainline them later on.
Nobody's asking for mainline submissions though. Just publishing the drivers source code under a FLOSS licence when they stop supporting it would be enough to let the community take over the maintenance.
The kernel side of drivers is already published under a FLOSS license, it's just that the code quality is usually subpar and the important changes are crammed into a tarball together with (sometimes) millions of other lines of changed code.
The sources for the matching userspace binaries (which are usually the issue for Android version bumps) are usually under NDA by the component manufacturer and can not be released by the OEM independently.
Is the kennel driver code not available for the Community to take over the process of mainlining? If that gets done then surely the user-side code will work with all future kennels that contain the driver?
The user-side will work with all kernels that contain the matching driver, but the user-side will not necessarily work on future Android versions without modification.