so, imo, the right thing to do is to add one more field (`last_post_subject`) to the "topics" table in the db, store and retrieve the correct value, and let the template designer decide what's clutter and what't not.
this will cost very little in code (change ~3 lines, add ~1), absolutely 0 effect on performance (the topic table is modified or read anyway), and completely negligible effect on db size.
[EDIT: it will actually require to change ~5 lines: i forgot the case where the subject of last post is changed with by an "edit" operation
it's an extremely simple mod, but it will make every template designer that decides she wants it to require code modification in order for her template to work. not nice.
again, this can hardly be considered "feature request". at most, its a tweak. (it is actually much smaller change than the half assed "author name in correct color" tweak that was casually added on aug. 21)
every other modern forum software i saw support it, and as the saying goes: "trilions of flyes can't all be wrong. eat sh!t"