Don't count on that for 9.4, that's too late for it (and that's not a
straight-forward problem). But, you can actually use a trick here to
support global sequence IDs:
1) define a view wrapping nextval for this sequence on the foreign server:
create sequence seq;
create view seq_view as select nextval('seq') as a;
2) On the local server, create a foreign table that scans the view already
defined in foreign server:
create foreign server foreign_seq_table (a bigint) server postgres_server
options (table_name 'seq_view');
3) Create on local server a function querying foreign_seq_table:
create function foreign_seq_nextval() returns bigint as 'select a from
foreign_seq_table;' language sql;

And now use each functions in local and foreign servers and you are fine
for the ID uniqueness. Note that you could also use an approach with
uuid-based methods to limit network delay across nodes as well.

No, there's no change in this area in 9.4.

regards, tom lane