While Egison has some powerful matching I fear it risks becoming a 'read only' language which is really hard to maintain. I would have to disagree with the authors that Elegance == Simplicity as they state in the presentation (Prolog comes to mind...). I wouldn't mind some extra lines of code that are easier to maintain unless there are clear performance benefits.

When used as a query language I would like to understand how Egison compares to past efforts such as Datalog or F-Logic which attempted to bring formal semantics and unification to queries. These were even more expressive than some of the Egison examples.