A bit of an aside: I wonder how much array-oriented languages like APL and J would benefit from being implemented on top of an interaction net machine?

I raised this in person to a number of array language implementors (and Connor Hoekstra) last year and they weren't familiar with interaction nets. I'm not sure that I was successful in convincing them that this was worth looking into, partially because I'm not yet personally convinced that this is worth looking into.