Co-dfns is interesting because I think it is the first compiler that has ever been written in a fully data-parallel style. But why does that make APL as a language particularly relevant, except that it was the implementation language?
I hesitate to answer this because I feel like 'arcfide's explained this much better than I can in one of his talks so maybe he'll see this and can point you to it, but if there's no response by the time I wake up tomorrow I'll give a detailed explanation on my views on this.
I'd love to hear your views, regardless of whether you can find arcfide's.