Hello there,
talking about jacktrip, there is a similar project providing this functionality. I used Jamulus myself now and then and it’s working quite well. If everyone participating focuses on the drummer (or one participant doing some beat) rather than the delay, it’s not so difficult to jam with each other.
Maybe it is an idea to have Jamulus integrated into Zynthian? (And then a Jamserver for the Zynthian community 
)
http://llcon.sourceforge.net/
Grooving Regards,
Bernhard