The maxlag-induced waiting time, as described in T244030, is acceptable in the “update” usecase, where inteGraality would spend a lot of time querying SPARQL anyways − definitely so in the periodic update, and mostly so in the manual update use case, which while "interactive" is expected to be slow.
It’s for the Queries (aka looking glass) feature, which is interactive, where the wait is not only unbearable, but also unnecessary.
Solution: cache the PropertyConfig at update time, to be used at queries time. I cannot foresee any situation where the queries would rely on an outdated cache, because a changed config requires an update to propagate to the cells and thus to the queries feature.
The only question is which persistence layer to use: serialize on disk as JSON? sqlite? mariadb?