The Tau are really the only race missing though. Everything else fits in well.

And you can stretch the Tau if you want.

But if you switch to a different part of the Galaxy you lose Stryxis, Rak'Gol, Yu'vath, Slaught and other FFG creations, which I'd gladly have instead of Blue Space Commies. And it's not hard at all to fluff them in anyways. In my RT games a Rogue Trader helped establish a Sept in Koronus, so now 180 years later the Tau can be encroaching on western Askellon.

FFG has already built their own cool little portion of the universe, crammed with more lore then even GW seems to have written sometimes. Starting entirely over doesn't sound that appealing.

But if you want, I don't doubt it would be easy to just say "Askellon is in Ultima", and ignore any Calixis mentioning fluff

And Askellon is much closer to the Eye of Terror, which is where most of the Big Deals of 40,999 take place

But if you switch to a different part of the Galaxy you lose Stryxis, Rak'Gol, Yu'vath, Slaught and other FFG creations, which I'd gladly have instead of Blue Space Commies... FFG has already built their own cool little portion of the universe, crammed with more lore then even GW seems to have written sometimes.

Then keep using Calixis , and don't require the new setting to be a Calixis knock-off. I'm just not getting the appeal of "Second verse, same as the first."

But you argument goes both ways, and keeping Calixis near lets you build on that history for Askellon.

And what we've seen so far of Askellon, it's quite different. Very isolated, few Inquisitors. It sounds like a grimmer setting

Gaunt. Dude. You took the words right from my mouth. I loved the Slaugth. They were a constant threat to my original group of Acolytes. They caused untold grief and injury. The depredations of the Amaranthine Syndicate were some of my favorite games.
I'll miss them terribly. If they could make an appearance in the new setting I wouldn't mind. That said, I also understand the need for Askellon to be its own thing.

Ideally, if we can't have the Slaught, Yuvath and Rakgoul back, I'd like a few new unique species to appear. My players get bored with the same old races.
And, of course, I'll always hope for the day when GW allows for the development of obscure races like the Q'orl, the Hrud and the Nikassar.

The Slaught don't make sense as archvillains.

They want to eat sentient creatures. That's it. Big deal. The Imperium recycles people into food all the time. The guys in Maggots weren't even harming anybody.

Moreover, why do they need a great villainous organization to do this? They just need to hang out in cemetaries.

There was a lot more going on with the Slaught than Necrophagia. The Amaranthine Syndicate was actively undermining the Imperium, sowing discord and war so that their masters could feed freely. They treated humans as cattle and the Higher-Castes could devour a living mind to gain knowledge. Whatever was going on with the Slaugth, they had a long history with the Haarlocks and they must have had some sort of relationship with the Yuvath - either antagonistic or otherwise. There's evidence that they have been distributing bio-weapons to xenophile heretics (the Vore weapon) and it's possible that they bioengineered the Sinophian Bore Worms. Slaugth flesh parasites can appear fully human, if a bit cold, and the Overseers themselves can wear the skin of humans to better infiltrate Imperial Society.

I used every scrap of material that I could find to expand upon the Slaugth in my first campaign, I eventually took some liberties with canon and suggested that the Slaugth were harbingers of the impending Necron awakening.

I don't know why the writers never went into more detail, maybe there just wasn't enough time. I remember a forum post from the old BI days where one of the original writers suggested that he had plans for them. He left shortly after the FFG change over, which may explain why we never saw much Slaugth stuff after Disciples of the Dark Gods.

And, of course, I'll always hope for the day when GW allows for the development of obscure races like the Q'orl, the Hrud and the Nikassar.

This, so much this.

Ideally, if we can't have the Slaught, Yuvath and Rakgoul back, I'd like a few new unique species to appear. My players get bored with the same old races.

And, of course, I'll always hope for the day when GW allows for the development of obscure races like the Q'orl, the Hrud and the Nikassar.

Absolutely- and if Askelon Sector is in Ultima Segmentum, of course it will feature a bunch of new sector-specific races. One more reason why I'm rooting for Ultima.

And no one has yet addressed my main point: if someone likes Calixis so much, why can't they keep using it , rather than require the new sector to be a rehash of Calixis elements?

(BTW- you can check out my take on the Hrud by clicking the NEW XENOS link in my signature.)

I'm totally okay with the new sector, I'm just lamenting the fact that we're moving on from the Slaugth. I loved them and they deserve a little more attention.

And no one has yet addressed my main point: if someone likes Calixis so much, why can't they keep using it , rather than require the new sector to be a rehash of Calixis elements?

As a matter of fact, I just recently upgraded my existing game to DH 2.0. The game takes place in the Calixis Sector and hopefully the Slaugth will make an appearance. I don't think anyone is demanding a complete rehash of what was done in the Calixis sector, some of us are just disappointed that there are so many unresolved plot threads from the original setting.

As for Askellon being in the Ultima Segmentum, I'm less convinced. I may be one of the few people who doesn't want his game to have to take place on the bleeding edge of 40K canon. The advance in timeline is one thing, being front and center during the lead up to the next Black Crusade is something else entirely.