[for the 822-impaired, please send replies to ietf-types(_at_)uninett(_dot_)no]
Personally, I don't have any problems with having a plethora of
top-level types for cases such as this. Apart from the meta-types
'multipart' and 'application', I always thought that the first part
of the type name was meant to distinguish between major 'media'
types - text, image, audio, etc-
The top level is supposed to give a clue to MTAs, gateways, etc.,
about the kind of media is being transmitted, so that it can choose an
appropriate encoding (say when translating from 8-bit transparent to
7-bit SMTP) or perform filtering based on the capabilities of the
destination environment, without knowledge of the specific type.
This is why chemical/* doesn't cut it -- because it doesn't seem to
require significantly different capabilities from the transmission
media or the destination environment than other top-level MIME types.
There needs to be a way to sub-delegate parts of the type space, but
this is best done by dividing the second part of the MIME type.
"application/chemical.foo" would be just fine.