Afaik, correct me if i'm wrong, a new LIST function will appear in FB 2.1
this function get some values from a field from some records (according
request parameters, filters, etc) and make a string: each values
separate with comma

if i'm correct, is a "reverse_list" function planned? (may be still exists)
the function could get a string of values separate with comma as input
and return a "list of values"... which make available something like:

select [...] from [...] where myfield in reverse_list(values)