You are correct. RestExpress does not support matrix parameter parsing. As I understand it, matrix parameters are not a standard--just a design idea from Tim Berners-Lee.
As far as a work around (other than the obvious switch to query-string parameters), you could write your own regex for the URL. Or you could supply multiple routes to the same controller method like this:
server.url("/services/test/1/detail", controller)
.method(GET);
server.url("/services/test/1/detail;{detailMatrix}", controller)
.method(GET);
I believe that would work, then you could parse the detailMatrix parameters in your controller method.
Hopefully that works for you,
--Todd