Depending on the pact, the Sanctum offers our heroes all kinds of bonuses, such as many different merchants, armorers and quest givers, as well as an innkeeper where we can bind our rest stone. By the way, you can't use all special pact reststones anymore, but only the reststone that belongs to your pact.
There is a new feature in the Primus' Sanctum that will be of interest to Death Knights who belong to the Necrolords' Pact. The developers have adapted the Sanctum to include a brand new Rune Forge, which allows Death Knights to change their weapon enchantments at any time via Rune Forge.
The Runemason was the creator of Frostmourne and Crown of Dominance. He is rumored to be the lost Primus. Source: buffed Since Runesmiths are part of the classic inventory of a Scourge stronghold in Azeroth anyway, it makes sense that the Necrolords of Maldraxxus have this feature as well. After all, the Burning Legion, with the help of the Dread Lords, smuggled Maldraxxi know-how out of the Shadowlands to equip the Scourge with the latest Necrolord weaponry. The lost Primus and Runesmithing ended up being the central point of the Maldraxxus story campaign. The fact that other pacts don't place rune forges in their Sanctum is self-explanatory there.
Also, a large portion of all Death Knights belong to the Necrolords pact. So, of course, the Runeforge is the perfect addition to the Primus seat. All Necrolords Death Knights can now conveniently imprint their weapons with any rune in their Sanctum. The Black Gate spell still remains the more useful way to change weapon runes, however, as you can use the gate to travel directly back to your starting location.