Doubtful they're interested in porting them over to be honest. There was an update where they accidentally included old files showing the team templates for Khorne but there was no models etc made. Think it was a case they considered it during Legendary Edition planning phase at the studio but went with the more recognised other eight instead (I'd have prefered Khorne over Elf Union which I feel didn't add much new but it is what it is).
Do we WANT a BB3? It was rough for too many vocal nit pickers regarding the transition from a complete BB to BB2 (and only 8 teams etc) despite the benefits. A wee update to BB2 would be awesome though but not sure it's lacking unless your after more teams and what have you or maybe an anniversary update with a special team jersey colour free to all players and some more decloned star player models (which appeals a lot actually - Big Bertha being male has always been a pet hate of mind esp as she's an Amazon accessable star who are meant to be all female).
The NAF is not the arbiter of what is or is not official in Blood Bowl - that'd be Games Workshop, the people who actually produce the game. The NAF is an unofficial organization of players that host tournaments and collect result data related to their dues-paying members.
And GW (or at least the gents that are in charge of the game now) said they had no intention of adding either team to the tabletop game.
So no, Khorne are not an official race (nor are Brets for that matter).
What's their take on Slaan these days? We had to get a literal re-skin just to get them in the game (albeit a very good one).
As for BB2 I'm sure if the devs want to add in CP, Khorne etc I don't think GW would get in their way too much and there's likely plenty enough demand for them if they think they're worth the time and expense in making.
The rumours of the other chaos teams coming true (Slaneesh, Khorne, Chaos Pact).
Turning off spiralling expenses in solo player.
That's it really, that and eventually all star players having unique models (some are off putting - Boomer is currently a Goblin instead of a Dwarf, Bertha is female but currently has a male Ogres model and head etc).