> people tend to want unique buildings that stand out

Just tell the LLM that you want a unique design. I've found LLMs to respond well to requests for "originality," at least in poetry, prose, and coding. No reason that can't do that in architecture as well.

> At some point an architectural design has to be built and you can't currently simulate real building sites at high speed inside a datacenter.

First of all, you can simulate a building site, or any physical environment. We've been doing that for years, even in games. AI companies are working towards a "world model" for precisely that reason. Second of all, even without a physical simulation, the laws of physics are deterministic and easy for an LLM to understand.

> The safe jobs are ones where there's little training data available online,

These cases are "safe" only in relative terms. Lack of easily-available training data is friction but not insurmountable. AI companies have bet big and they have a strong incentive to find and use appropriate training data.