In the topic What is a note of type Link?, I posted a table of note types which may be of interest.
In particular we use the SOURCE_TEXT type to store the contents of the Gedcom SOUR.DATA.TEXT tag.
The CITATION type can be used to store formatted citations.
The LINK type may be appropriate for the WWW tag. I’m not really sure. Perhaps this would be better stored in a source attribute? A web address together with the accessed date are citation elements.
A PLAC tag under the PUBL tag is actually quite a good idea. Publication information often consists of a publisher’s name, place and year of publication. We may decide to store this information separately in Gramps when we enhance the citation formatters further.