We don't have all of Cyrodiil on ESO yet, but we already have plenty to compare locations that appear in both ESO (2E 582) and TES IV (3E 433). The infrastructures that I have selected are mainly the forts and capitals of the imperial counties.

* In 747 years, several forts have remained in ruins. It is possible that most have been restored and put into service in the meantime.
* There are forts existing in ESO's time that will disappear 747 years later. And vice versa with forts that will be built after ESO.
* All of the forts in TES IV are in ruins... No wonder the Septim Empire was in decline.
* ESO, like TES IV, is not representative of the facts. They are only sketches of a much larger Cyrodiil with many more towns and forts.
* The base game emphasizes the influence of the Second Empire through its ubiquitous architectural style. As well as a "human" style used on base game ruins across Tamriel.
* The Colovian houses architectural style in ESO is very similar to the architectural style of the city of Chorrol in TES IV.
* The Nibenese architectural style in ESO is a cubic version of the architectural style of the city of Anvil in TES IV.
* Leyawiin's Tudor architectural style extends beyond the borders of Blackwood in ESO. The ramparts and towers seem generic (currently extended throughout the Nibenay).
* Forts in the base game may be "obsolete". I am referring to Fort Grief even though it is not visible without off-map in ESO's Cyrodiil map. Fort Grief in the base game adopts the style of human ruins and is close to the visual of TES IV in its layout. The Deadlands DLC significantly modifies the fort. When Nibenay is released, it will be logical to find the same visual from the mouth of the Silverfish.
* I think Nibenay will adopt the same fort style as Blackwood. Maybe also for Colovia. But I suspect Colovia will have forts in the same style as Skingrad. Note that Skingrad had uniquely styled walls in TES IV.





It's not impossible that if the Cyrodiil zone or the Gold Coast were released today, the visual would be very different. I'm all for keeping the core game styles that have their own lore and logic imagery from a bygone era even if it's not always perfect. But a mix with the new styles would be nice.
In the selection above, some structures are accessible through Battleground or quests. It's hard to say if ZOS will significantly change their visuals when they're visible from their respective regions.

A comparison of throne rooms.