I noticed today that our data types APIs (org.apache.spark.sql.types) are actually DeveloperApis, which means they can be changed from one feature release to another. In reality these APIs have been there since the original introduction of the DataFrame API in Spark 1.3, and has not seen any breaking changes since then. It makes more sense to mark them stable.
There are also a number of DataFrame related classes that have been Experimental or DeveloperApi for eternity. I will be marking these stable in the upcoming feature release (2.1). Please shout if you disagree.
