I know that why you focused on XML, even the majority in the industry have realized that XML is better than Graphs (even Triple)
However, XML inherently has some issues, which one of them is the size of the file for “data/information exchange” which even IFC (in all formats) and all “closed file formats like RVT” have
And your approach is this (something like microservices):
There are lot of issues, which can list, for instance “rule checking” in XML which maybe be solved with Schematron
But still there are lot of obstacles 