The mismatched mount mess

You know, what annoys me about that fsdevel thread is that presumably clued people do not bother to RTFM. Or RTFS. Or directly experiment. FYI: suid/nosuid is mount property. There is nothing to "conflict" - you either pass MS_NOSUID to mount(2), or you do not. Either way, it affects that mount and nothing else. Filesystem itself doesn't know and doesn't care.

All of the above could be found in a couple of minutes by reading through mount(2) or mount(8) and experimenting.
As in,
root@kvm1:~# dd if=/dev/zero of=/tmp/foo bs=1M count=2
2+0 records in
2+0 records out
2097152 bytes (2.1 MB, 2.0 MiB) copied, 0.00372987 s, 562 MB/s
root@kvm1:~# mkfs /tmp/foo
mke2fs 1.44.3 (10-July-2018)
Discarding device blocks: done
Creating filesystem with 2048 1k blocks and 256 inodes

Allocating group tables: done
Writing inode tables: done
Writing superblocks and filesystem accounting information: done

root@kvm1:~# losetup /dev/loop0 /tmp/foo
root@kvm1:~# mkdir /tmp/a /tmp/b
root@kvm1:~# mount /dev/loop0 /tmp/a
root@kvm1:~# mount /dev/loop0 /tmp/b -o nosuid
root@kvm1:~# cp /usr/bin/whoami /tmp/a/
root@kvm1:~# chown lp /tmp/a/whoami
root@kvm1:~# chmod +s /tmp/a/whoami
root@kvm1:~# /tmp/a/whoami
lp
root@kvm1:~# /tmp/b/whoami
root
root@kvm1:~# umount /tmp/a /tmp/b
root@kvm1:~# losetup -d /dev/loop0
root@kvm1:~# rm -rf /tmp/foo /tmp/a /tmp/b

Two minutes, beginning to end. Sigh...