A couple of vendors have asked for the ability to change the "request type" of an issue via REST.
Its a somewhat tricky problem in that an request type represents a bunch of "field values" and a workflow via the associated issue type.
We could however allow for "easy updates" say where the issue type does not change.
A lesser problem is one of issue consistency. Eg Request Type X has 3 fields and Request Type Y has 2 fields and 2 defaulted fields.
If we change an X into a Y then the fields will not be consistent in value.