As @Sam Ottenhoff says, this issue is fixed in SAK-34477, so I close this one as incorporated.

FIB had custom delimiters added in https://sakaiproject.atlassian.net/browse/SAK-34477#icft=SAK-34477

Would it be possible to also add a delimiter to Fill in the Blank '|' pipe character?

@Shoji Kajita has uploaded a patch in the duplicate JIRA https://sakaiproject.atlassian.net/browse/SAM-3215#icft=SAM-3215

It's a really simple patch. I'm not sure if it covers all the use cases but if you think it does, maybe this long time issue could be fixed.

Trying to think in the final user best option (and forget from now about the complexity of the development) I like Paul's idea of "per-question" delimiters, with curly as default, but allow to select a different delimiter if you are going to use curly brackets. I think the best option is to allow the user to set their own delimiter (because if we offer only some options we can arrive to a point where no option is good for the user)

So each question should store the specific delimiter and use that to process the test. Curly brackets as default, or the user's one if that option is selected.

Now, returning to the "real world" where we need to develop this. We can add the char in the itemmetadata table, so we don't need to modify the database, and quickly check if there is a "DELIMITER_CHAR" field in the item metadata and pick the delimiter to process the itemtext and if not, then use the default one. This doesn't seem so complex...(surely until we try to do it).