I fully understand this, but the implementation is a bit short-sighted. It would have cost nothing to store XML in an XML Postgresql field, instead of as text. It's probably not extremely fast to filter on un-indexed items, but it is really easy to implement.
I always use Shiny as frontend, because I am fluent in R, but handling ruODK update via a local warehouse is made rather complex currentyl because of the limited filtering abilities.