A SIP proxy and a SIP application server have completely different
positions in an architecture (also IMS).
SER is a SIP proxy with modules and tools (including SEMS) that also
can be used to implement many applications. As such, SIP CGI is
probably a more likely new module for SER than a JSLEE.
However, if you look at using SER and Mobicents in combination, it
would be very interesting with a how-to on iptel.org... ;-)
g-)