Huh… so you guys would prefer if policies and beliefs just stuck to X yield bonus on Y building kind of invisible boosts, and never tried to add any unique infrastructure or units that would require art assets like icons and models, and make a tangible impression on the map? Do you take issue with the worship building beliefs — mosques, cathedrals, etc. — added in civ6 which disjoint religious architecture onto the religion itself rather than the cultures?
Let me shake the straw out of my hair so nobody except you turns my comments into a Straw Man argument for something I never mentioned.
Civ is a computer game, no matter how much they try to stuff it into a board game mold. Computer games are graphic representations of their subjects, so OF COURSE every chance the game has to put a graphic representation of something out there, it should.
BUT tanks and aircraft do not have ideologies. Let's just make sure when selecting an 'iconic' ideologically - or religious - based Unique we don't do it the lazy way and perpetuate unrelated stereotypes as Uniques. The game should be better than that. More importantly, they have the resources to do it all better than that.
So, IF the T-34 is going to be a Unique Unit, it is a Russian or Soviet Union Unique, not a generic Communist Unique. Nor is Fascism indelibly linked to Stukas, except German Fascism based on the Prussian
Bewegungskrieg military tradition.
The ideology can, however, be linked to some kind of militant Political Military force, like the SS or SA or Italian Brownshirts - just don't try to use any historically-accurate symbolism like the swastika or you make it impossible to legally sell in parts of the world and highly controversial almost everywhere.
Twentieth century Fascism and Communism both had a hankering for Monumental Government architecture that ignored the human scale and element, so you could have Unique city graphics for the capital of an ideologically-oriented Civ.
Another thing that is also very, very present in the modern Ideologies is their constant and ubiquitous display of symbols: the Nazi or (Italian) Fascist, Soviet Communist or even Democratic party/national symbols are everywhere in those states. Again, don't use real ones unless you want to get into serious trouble, but make up a suitably innocuous geometry/color combination and when you adopt the ideology it suddenly sprouts on your flags, buildings, ships, units, etc. Since many modern Ideologies are substitutes for religion, they could sprout on the iconic Religious Unique you were using, which might also sprout discontent/disloyalty among your population . . .
Religions and their 'iconic' structures, to my way of thinking, are not as tightly linked. Virtually all religions needed a place to worship in groups. Some wanted places elevated to be 'closer to God(s)' (Pyramids, Platforms, Mounds, etc) most wanted awesome structures to reinforce the proper respect for their Diety (Gothic Cathedrals, the Great Mosques, Wats, Stupas, etc). I think Civ VI got this Right: put together your religion from elements, pick your iconic structure if you want to - maybe in Civ VII broaden the choices, to include Sacred Groves or Henges, Hermitages, Monasteries, Minsters, etc as religious OR civ Uniques: there's a lot of religious architecture to choose from out there.
Something similar could even be used for the late-game Ideological religious substitutes: pick from a bunch of ideological traits, which include one or more Unique elements, civilian or military policies, Units, Buildings, in addition to the ubiquitous banners and symbols. IF I want to play Fascist though, that shouldn't mean I automatically get Stukas or PzKpfw VI tanks, but it might mean I get Puce Shirt Fascist security forces (for free or on the cheap) which can be used either to increase Loyalty in my territory or can be armed as Elite regular troops with tanks and other weapons and go into battle with better attack factors or some other advantage.