IMHO there is ONE game that would allow easily a Dune mod ... not SEIV, but "Emperor of Fading Suns" !!
This is an old (97) game from HDI, it is quite good and has already a Dune feeling, focuses on noble houses doing planetary development and ground combat, AND is very moddable !
It's available for free at
www.the-underdogs.com , and there are still some activity around it, try this link :
http://www.kborek.cz/official/efslinks.html
However it doesn't provide Guild Transport feature ...
