This is related to T103030: Expose Flow history in API, but not quite the same thing.
To be determined if this should be an option to ApiFlowViewPost (probably) or a separate API.
This functionality is available in the internal API from at least one path already, single-view. See https://www.mediawiki.org/w/index.php?title=Topic:Sjbg86fqz4m00em9&topic_showPostId=sjbg86libif817up#flow-post-sjbg86libif817up , https://www.mediawiki.org/w/index.php?title=Topic:Sjbg86fqz4m00em9&topic_postId=sjbg86libif817upseq732h45hsh44qj&topic_revId=sjbg86libif817up&action=single-view , and https://www.mediawiki.org/w/index.php?title=Topic:Sjbg86fqz4m00em9&topic_postId=sjbg86libif817upseq732h45hsh44qj&topic_revId=sjhhx9elln2stjky&action=single-view .
Although that page is pretty minimal, it looks like it's all there internally (see renderSingleViewApi, RevisionViewFormatter, and RevisionFormatter).