This seems like a really cool and useful idea. Are you sure it would be that long to develop a prototype?

I'm sure that it would take me very long, not being an expert in any of the required skill areas and all that. Seen from afar i identify several key components of a high quality architectural aging simulation: water/geometry interaction (most stains seem to be related to differences in water exposure), some rough thermal simulation (different drying speed, often you see "shadows" of internal structure on the outside, because the internals influence heat dissipation and thus drying speed), gathering and refining actual aging examples for all kinds of surface materials and finally extracting not only geometry but also surface material information from the input formats you would want to support. Putting it all together to generate output models or images would be the smallest part.

A less sophisticated effort might just try to use image based rendering techniques to normalize before/after photos into flat textures ready to be used as a learning set for some ML magic. Unfortunately, this would completely fail at respecting different aging properties of surfaces that look similar when new. Cleverly alternating between initially similar surfaces could for example be harnessed to get a clean, minimalistic look when new and expose some ornaments that distract from unintended unevenness later.

This isn't a completely theoretical idea by the way: a ca 2005 subway station here that used to get heavily criticised for its bland white walls is slowly starting to expose fascinating watermark-like images embedded in the texture of the walls, consisting of cleverly modulated ribs that seemed perfectly uniform when new.

Have you got any examples of concrete building that have aged well? I know some buildings age well but none I can think of are made of concrete.

(I like the software idea, as aging is something that architects would appear to overlook in any buildings built in my lifetime).

Sorry for the late answer, and sorry for the lack of pictures: I originally noticed different qualities in aging at university, where amidst many examples of terrible aging one lecture hall building and one office/former residential stood out. The lecture hall had a broken rib surface like one of these https://www.reckli.com/en/products/concrete-patterns/ribs-wa... (e.g. "Sicilia") on the larger surfaces which turned the staining of time into a feature, the office/former residential was a framework of concrete (probably modular), filled in with grey sand/lime bricks of similar brightness, but slightly warmer hue than the concrete that gave it a subtle elegance (in my eyes, others hated it) that seemed to be immune to aging.

Not exactly an example of aging well, but nonetheless deserving of a honorable mention: all the old Flagler Hotels that now form Flagler College in St Augustine. They were pretty much making up the modern use of poured concrete for houses as they went and it does show in many places. Most of the concrete surfaces are looking rather rotten by themselves (despite what i suspect to be quite intensive maintenance), but the crazy playfulness of all the decorations that surround them do a surprisingly good job at distracting from that. You notice, but you don't care.