Doing so runs into races with filesystems which make half-constructed vnodes visible to other users, while depending on the chain vput -> vinactive -> vrecycle to be executed without dropping the vnode lock.

Impediments for making this work got cleared up (notably vop_unlock_post now does not do anything and lockmgr stops touching the lock after the final write). Stacked filesystems keep vhold/vdrop across unlock, which arguably can now be eliminated.