I've done this where I work. We needed to add attributes to tables, table columns, and table columns in a specific context (e.g., list view, search controls, single record preview, etc). It is nice for semi-technical internal users. The thing that becomes harder is deployments, because now you need to sync not only code, but data as well. When I get a chance, I plan to make it so all of the data can be synced to and from text files (e.g., toml), and run that as a deployment step for at least some of the data if it can be maintained in text.

Interesting that the article you pointed to uses EAV as an example of an inner platform effect. We didn't use EAV, but it isn't obvious to me that it would be a bad idea in this context.

It still makes enforcing relations harder in the metadata context; stuff like "The table_name col in the load_history table needs to reference an existing primary key in the table_info table" is not easy to jam into an EAV table

Yea but there are benefits like being able to add new attributes at runtime. So might be worth it in some cases.

I might be missing what you're trying to do but some databases allow you to add text as metadata to DDL objects. You don't mention which database you're using but PostgreSQL allows you to add COMMENTs to database objects (schemas, tables, columns etc) using syntax like this:

COMMENT ON TABLE <schema-name.table-name> IS 'This is a comment on a table.';
COMMENT ON COLUMN <schema-name.table-name.column-name> IS 'This is a comment on a column.';