the saga isn't over since most have yet to experience it at home. (and technically a saga's episode is ongoing until the next KOF begins, or a person quits playing it.)
There won't be more bosses added to home version,
but they will add more stuff to KOFXIII home version,
and at least one new playable character the arcade version doesn't have, it's very possible.
And you mention "from scratch" but you have no idea what's going on in SNKP.
They are likely still working on sprites to add 1 or more characters exclusive to the Home version.
It's happened with XI, XII (even with the long process) and it can happen with KOFXIII. Elisabeth and Mature were kind of rushed but they were still very playable and competitive worthy even though they were lower tier.
SNKP is definitely working on finishing at least one more character to be ready for the home release. It might be from Those from the Past, but it definitely won't be a headswap. Neither Elisabeth nor Mature were headswaps in KOFXII.
sigh, some people really forget recent history. One or more exclusive characters in KOFXIII home version is as possible and obvious as including console exclusive options accessible to the player. Characters take longer but it's really clear SNKP isn't sitting on their hands right now.
They are preparing content for KOFXIII home version, whether it's 1 or more characters, someone new will be added. For now they want the arcade to sell,
so the more time they delay the home version, the more time they have to add more playables. http://www.neo-geo.com/forums/showthread.php?t=200269
there were about 7 unnamed slots on KOFXII disk (3 of them must be K' Team.)