I doubt that DM3500s will get the new DDU.
2809 got it a month ago. Tridents and gassies have them too, the
oldest batch of bendies also have them.
From your posts, I really think you need to go out, perhaps to
the west and see for yourself a few things:
1) New SG plate Wrights being used on Jurong industrial, a lot
of them may not be stated as perm on sgwiki but they have been on
the same services for quite some time. This is in reference to your
posts on slbp having too much spare DDs.
2) Which buses have the new DDU.