Jewel of the North
Matt Colville has the Strongholds & Followers pretty covered doesn’t he? So unless that product bombed(?) it would be good to focus on fresh terrain, which fortunately aligns with where most of the interest in the survey lies.
It did not bomb, but it was a little far from what some expected. The rules were ok, but they did not mix that well with the 5e rules. Like the Followers have a special ways of gaining level, use wounds thresholds to instead of hp etc. Also some rules entry only point you to rules that are not in the book and will be covered in a OTHER book that is not yet finished. Also, the strongholds and their benefit to the classes were pretty unbalanced.
Its not bad and its pretty usable, but it feels like its own system that happens to sometime use a d20.
I think A5E could do a LOT better by using the rules from 5e and have the retainer/domain rules interact in meaningful ways with them.
My idea would be to use the ship rules for strongholds, having them have the same stats as a character and a bunch of different parts that can be manned to use different actions during a fight and using the Mob rules from the DMG to represent the different units of an army.