For instance magic_quotes_gpc has been deprecated as of PHP 5.3 but will not be removed until PHP6. In PHP6 is short_open_tag set to be removed or deprecated or neither?
Whether it's appropriate to use short_open_tag has already been debated ad nauseam - I'm really interested in the the official stance of the PHP core developers. The PHP documentation doesn't list short_open_tag as set for removal or even as deprecated.
The Jury seems to be still out on this one.
According to this entry (by Rasmus Lerdorf no less!) in the PHP internal mailing list, they are at least not removed in PHP 6.
Read through the conversation, it seems as if there are very differing opinions even among the PHP internals (provided the people posting to that list all are on that team, which I assume but don't know.)
It was suppose to be removed, but it hasn't been. Considering that it's considered a bad idea, it's best to just set a standard for yourself, which is "just stop using it".
Keep in mind that the same fate happened to magic_quotes, php global vars and the eregi functions. Albeit those were removed for security and speed reasons, but when something becomes recommended not to be used, PHP has a history of removing it.