DLC is guaranteed. DS1, DS2, DS3, Bloodborne.
As for milking the cow...I don't think Bandai Namco is gonna let the biggest cow that has presented itself in decades to go away without some good milking. They've put the money and faith in the Soul series even when Sony balked. Now it's pay day, and they'll try to keep it that way like all publishers do.... Ubi with Acreed, ABK with COD, EA with FIFA/Madden/BF, Take Two with GTA etc.....
The formula will eventually become fast food. I'm just glad I was able to experience the natural progression at its best.
There is room for expansion with the Sekiro formula. The Souls formula is going the way of the doo-doo. Whereas for casuals the series is just starting for them, for me I'm already deep into Souls fatigue. At this point I'll probably plat any future titles cause every other title to come before I've already platted.