The devfs would eliminate the overhead and reduce the umsdos requirements. When a pty is needed, root must change the owner. When that pty is not needed anymore, root must change the owner back again. There are problems with that method, because it means that many programs should be setuid root. Emacs shell windows leave a security hole because the pty owner never gets changed.
Many programs can fail to change the pty owner back.
With devfs, the kernel can chown ptys back to root when a process does not need them anymore. The kernel might be able to let normal users chown their own pty or it might perform the chown automatically. The devfs could appear to contain only those devices that the user has permission for. The devfs could always seems to have just the next available pty instead of all the ptys in use. Kernel bloating There are always tradeoffs.