“Complete pieces of music” is only one use case for flows. For example in Dorico, this page would have two flows on it, one of them displayed twice in separate frames. http://www.henle.de/blog/en/files/2013/01/Beethoven_Sonata_21_Opus_53_Seite_1.jpg
Dorico has got it right IMO. integrating “heading” text as part of the flow is the wrong logical place for it. If you wanted to integrate it anywhere, the layout would be a better idea (but still a bad idea).
You might need to display the text anywhere in the score in any format you want, perhaps multiple times (e.g. in a table of contents, an index of themes, etc), or maybe not display it at all.