I like the idea of a more aggressive Civilization game, and pulling some of the buildings out and putting them directly on the map for more unit interaction is something I'm looking forward to
Slight tangent, but I felt that pillaging in Civ5 was fairly underpowered. It's totally worthwhile to pillage great improvements and luxury/strategic resources! But those were very specific tiles, and pillaging anything else had very little benefit. As far as I can tell, the only relevant combat in Civ5 was basically how well one could take down a city. In particular, if one prefers to keep the city slightly more intact, it's more worthwhile to just leave the improvements alone and take the city directly. The Danish were supposed to excel at this harassing strategy around pillage, but I never felt it was very realized.
At least in Civ6, it looks like the positioning and prioritization of districts will lead to a lot more nuance over just taking a city down. There was no explicit mention of this, but there appeared to be a harbor district which allowed the land locked Chinese capital to make boats out to sea, so wanting to take advantage of sea tiles is no longer as binary a choice (in Civ5, your city is either on a coast or not). Placing an encampment/barracks district right at one side of a river on a road leading to a city also seemed fairly novel; it guarded the most direct way to the city, and allowed units to be deployed to a direction where they'd most likely move anyway, so to save some turns on movement it would make sense to have the barracks there.
Not that this'll happen, but I hope that the strength of a city's attack power will actually be affected by the number of improved and/or pillaged tiles within its radius. If this needs causality, perhaps the number of worked improvements/districts that a city has gives it the necessary supplies to feed and arm itself, and cutting off said supplies will cripple its ability to fight back.