Personally, I sort of see "Helix" as its own brand, almost separate from other Line 6 products, and the name carries a lot of familiarity and weight—which is the whole point of branding. So presumably, if we ever get around to making a new flagship, I can only imagine it'd have to be called Helix Something... Or Something Helix. But not "Helix 2" or "Double Helix", because those names are lazy and dumb.
EDIT: Lazy and dumb for Helix. Absolutely nothing wrong with putting a number after one's product. <cough> DL4 MkII, AxeFX III <cough>