Well, in IN, I recall that J.C. existed -- but celestials either don't know his True Nature, or if they do (OH HAI YVES!), they aren't talking. So unless I've timeline hopped again, that statement is canonical.
Personally, side-slipping timelines is (obviously) something that intrigues me. It can be done for (mostly) humor:
http://homepages.tcp.co.uk/~maya/nomine/fiat.html, bottom of the page, series marked "sliders." (One of the ones that amuse me most contain "Dominic, Archangel of Creation" and "Eli, Archangel of Judgment." (Also Jordi, Kyriotate Archangel of Lightning...) My other favorite is Tech Heaven/Nature Hell, with the GodHackers of Judgment.
It can be done with... hm, more enigmatic stuff; I had Vapulans collaborating with Yrth "dark" elves, opening a portal which the angels busted -- but which got the angels stuck there. Then an elf tried a Banish, got a 111, and perceived the angels as, well, servants of the whatever-it-was Yrthian elves venerated. (I'm blanking on the term.)
And then I did IN IOU, which is both fluffy as heck, but can also have serious bits.
Basically, I do think it's possible to do multi-world stuff and continuing to incorporate the elements of In Nomine that resonate with the GM and players. The GM (and players) just have to figure out what those elements
are and how to incorporate them. (In my case, the meta-universe idea for IN Yrth was that God had
many universes going, which were presumably all accessible... from the Higher Heavens. Any Archangels exclusively in the Lower Heavens were out of the loop. Yes, this did mean that Uriel might've been reassigned (or not!), and Yves might've shown up if they'd gotten lucky. In the meantime, they had to track down some Vapulans and figure out how to get home...)