I know of one guy besides Qui-Tom that has two. His are pyrestone and RGB, but to my knowledge he hasn't said anything about coupling them. Be interesting, for sure.
Hmm I wonder who this person your referring to is hmm??? =P
Anyways if u are referring to me. I have not really give it much thought since the style of the each saber is different and it would be off balance. RGB Weights a little More then the Pyrestone one. Likewise, unless I get shorter blades dueling with it would be tough since the saber tip would no doubt smack the ground if I was to try to duel with it hahaha. I'm 5'8" btw and if u factor the length of the hilts plus two 36 inch long blades you can see what I mean. =D
Interesting idea though. Now I have a excuse to order a Dark Violet MLS along with the coupler hahaha.