These are still very vague except for the Dark Angels section of this, but these rumors have Dark Angels coming in a future boxset faced off against what may just be another Imperial Force of some kind.
The big part of this is the Primaris Dark Angel HQ in the box.
Please remember that these are rumors. I have not yet heard anything reliable regarding this box set and I can only assume its a ways out still.
via Bell of Lost Souls
https://www.belloflostsouls.net/2019/04/40k-rumors-more-on-the-lion-upcoming-set-and-his-foe.html
- The boxed set is reported to be another one of these boxed sets like the ones above.
- The Dark Angels are one of the two forces in the box.
- Look for a new Primaris version of a Dark Angel HQ in the set.
- More conflicting info on the opposing force says it is either Imperial in nature, or based on the Aquila in some way.