I added a new section at the bottom of your RFC. It contains statistics from which I conclude that using ENUM would be a good alternative.
Topic on Talk:Requests for comment/Content model storage
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Hi,
Using an enum is not feasible. First off, the page/revision/archive tables are in MediaWiki core, and should not contain any references to extensions (Flow, Wikibase, Scribunto, etc.). Currently any extension can define arbitrary content models and formats, like MassMessage's MassMessageList content type (example).
Also, using an enum also means we need to do a schema change any time we wish to add a new content model or format.
Finally, I would have preferred discussing your alternative proposal on the talk page before we added it to the RfC. I've removed it from the page now because it doesn't fit our requirements.