We propose to remove the following exports from GHC.Exts:

data BCO#
mkApUpd0#      :: BCO# -> (# a #)
newBCO#        :: ByteArray# -> ByteArray# -> Array# a -> Int# -> ByteArray# -> State# s -> (# State# s, BCO# #)

These functions expose extremely low-level interfaces which are likely to leak unstable implementation details to the user. To avoid future breakage, we propose that they be only accessible via ghc-internal after a deprecation period of one GHC release.