Apart from it being an interesting technical challenge or hobby is there any mundane practical reason for creating An Algol 68 compiler?

According to https://algol68-lang.org/, and as expressed in the recording, the contributors (specifically Marchesi) believe that ALGOL 68 continues to have advantages over other languages to this day ("more modern, powerful and safe" and "without successors"). One mentioned in the video is that the more complex, two-level grammars allow properties that would usually be described in the semantics of a language to be formally expressed in the syntax (the example he gives is the behaviour of numeral coercion). I guess this is not a surprise, as van Wijngaarden grammars are known to be Turing complete, but nevertheless it seems like something interesting thing to investiagate! There is a lot of lost wisdom in the past, that we dismiss because it doesn't fit into the language we use nowadays.

I'd love to be corrected, but my intuition tells me probably not.

The only pragmatic use for a modern Algol 68 compiler I can think of would be to port a legacy codebase to a modern system, but any existing Algol 68 codebase will likely see greater porting challenges arising out of the operating system change than from the programming language.