Obviously, all conjecture...
M&B 2 Setting
1) It will not be Calradia. It won’t be fictional. It will be a quasi-realistic setting. Source: Search for a podcast by “Just Press Start” with TaleWorlds’ Mika’il Yazbeck – when discussing future settings he says there is a higher demand for real settings, and that TaleWorlds will not return to a fictional land in future iterations of M&B.
2) It will include Naval warfare, therefore the land will have sea-going areas, possible islands or major rivers. Source: Caribbean!, the M&B new DLC has a large emphasis on naval warfare, and the programming has been done by TaleWorlds (see interview with Caribbean! makers). No reason why they wouldn’t include this.
3) It will be medieval, middle ages. Source: PC Gamer interview.
4) The infantry unit in the teaser trailer is wearing a classic Norman helmet. Features include a strong nasal protection, with chain-mail around the back of the head.
Guessing: it’s based in and around the Norman conquest, 11th century – British isle/Normandy etc. Or possibly a Nordic theme around Scandinavian themes – Kingdom of Denmark/Norway etc. This would deliver on the naval potential, and date it around the right era. Or Anglo-Saxons (e.g. King Cnut...make sure you get the spelling right

) vs Scandinavians (Vikings etc) – this would be a bit earlier (9th/10th centuries+).
Personally, I hope that it is a fictional setting, as there is more scope for an interesting/original landscape design...but just preparing people for what is likely...