It appears to me that --allow-keywords in mysqldump cannot have any use. Of course it's hard to prove an absence of scenario, so I may be missing something.

From what I see, it is used in 3 places: twice interchangeably with --quote-names, to define the value for SQL_QUOTE_SHOW_CREATE (one of these occurrences seems to be ifdef-ed out); and once on its own to decide whether column names in the table definition must be prefixed with a table name, which is apparently the whole idea behind the option. But

• if --quote-names is turned on, there is no need in --allow-keywords as the identifiers will be quoted anyway;
• --allow-keywords cannot really replace --quote-names (cannot be used without it) when data is also dumped, because if a keyword is really used for a column name, without --quote-names mysqldump fails on SELECT from the table, trying to use the unquoted name;
• so, for the option to play a role, mysqldump must be run with --skip-quote-names --no-data;

• even in this case, it can only get to its target logic if SET SQL_QUOTE_SHOW_CREATE fails on whatever reason (and if mysqldump runs with --force, otherwise it will just abort);

• even if all this happens, the route it takes is apparently designed for --xml execution, and the table structure it ends up with is likely to be invalid, regardless whether it uses keywords for column names or not, e.g.:

CREATE TABLE `t` (

  `t`.`i` int(11) DEFAULT 'NULL'

)/*! engine=InnoDB */;

(which further fails due to a wrong default value).

So, all in all, I can't find a scenario when it would work. If it exists, maybe we should update documentation to indicate it.