(Sexps are usually not my first choice, I think it is a "lazy option" for people who do not want to write parsers / design their own syntax. Even then, they are better than current Nix expressions).
There are some real advantages to having one universal syntax: witness the explosion in XML and, later, JSON (both of which are generally inferior to S-expressions[1]). It'd be pretty great for one person to write one parser, and then everyone forever after to be able to use it. We'd be able to focus on semantics and not on syntax.
[1] Although it is nice that JSON supports first-class associative arrays.
It's a volunteer-run service. It makes sense they don't want to host your proprietary binaries
(I don't see what's wrong with adopting sexps to avoid dealing with custom syntax -- quite the opposite,)
Anyway, thanks for the answer