Interesting article. If we don't restrict to Unix-compatible userlands, there are many more impressive operating system kernels written in Pascal or its descendants, e.g. the UCSD p-System, Lisa OS and the Classic Macintosh OS. Windows at least used the Pascal calling convention in its 32 bit versions (though the system itself was not written in Pascal).
Gave it a play on QEMU, seems the latest image of Gloire (A simple UI variant of Ironclad) is not wanting to boot on my QEMU. Will give it a few months and play with it again, looks interesting enough.
Would definitely be an interesting contender for use in safety-critical environments where Ada/SPARK are favored.