I made a post in a similar topic month ago : Some DLC concepts with the same pattern as LotW and DotD - #224 by CouguarLoup7693 You can read this post, I made 13 proposals.
So I will update this post.
Barbarians of the Mediterranean
A DLC centered around late antiquity western Mediterranean Sea.
Introduce the Suebi and the Vandal and the Lombards
The Vandal fight against the Roman, byzantine, suebi, wisigoth, berber during their long journey to Tunisia
The Suebi moving to Iberic peninsula and setting a kingdom here.
The Lombard conquering Italy
A last Roman campaign (Originally I proposed a byzantine campaign when Belisarius and Narses have conquered the ostrogoths and the vandals. But now we have the Roman civilization and he is better to put a romain campaign in this late antiquity DLC)
Renaissance DLC/ war of Italy DLC
(Originally I proposed a mountain DLC with Swiss and Georgian but now we have this last civilization)
Venetian (two obvious UU : galleass and stradioti. We can ever make a Skanderberg campaign)
Swiss (important player in late Middle Age and Renaissance)
Papal state
Charlemagne DLC
Introduce the Saxons and the Lombards
One campaign for Charlemagne and two for the other civ