For ease of migration, we should consider having javac emit a warning rather than an error, when old/retired -source and -target options are specified.
Comments
Note JDK-8011044, which added a warning into JDK 8, to warn that support for the older options, including 1.4, would be removed in a future release.
17-01-2017
After due analysis, this is likely to cause more problems than it fixes. Partly, this is against the policy of JEP 182, but more significantly, the code for supporting 1.4 has been removed from javac, so we would either have to replace that code (completely negating JEP 182) or else treat 1.4 as "something else", such as the "oldest supported version", which could cause syntax errors if the code was truly intended for -source 1.4.