the debdiff can easily be adapted but if you want to do the xenial SRU that would be welcome, the team working on the GNOME3 ppa should be able to use the yakkety debdiff or adapt don't worry, also you probably don't need to bother much using VMs and build/testing on each serie, just get the source for xenial, do the change and generate a debdiff using whatever version of ubuntu you are on, for those sort of changes it should be safe enough and the sponsor can test before uploading
the debdiff can easily be adapted but if you want to do the xenial SRU that would be welcome, the team working on the GNOME3 ppa should be able to use the yakkety debdiff or adapt don't worry, also you probably don't need to bother much using VMs and build/testing on each serie, just get the source for xenial, do the change and generate a debdiff using whatever version of ubuntu you are on, for those sort of changes it should be safe enough and the sponsor can test before uploading