As evidence of this: See Primaris Marines, created out of nowhere because they wanted to make better looking Marine models.
They succeeded
IMO, I just wish they could ride in transports and had more customization options than they do.
So them coming up with a new "standard guard kit" based on the Cadian armor set is very easy to come up with and, in this new era of
40k, easy to justify as well.
I think this is the route that
GW will go for Guard-- a single line, with other lines being relegated to upgrade kits or forgeworld.