this is a very interesting question.
being able to actually precisely position separate addons or connect them (as in dps meter is always 10px below player unit frame) is the last piece of the puzzle before I feel comfortable with releasing my own UI. I'm using couple of custom scripts to anchor one frame to another, but having an addon that does that in bulk (and lets me change profiles for different layout would be awesome).
as far as I know there is no such addon but maybe one of our more skilled addon makers might want to write one?
to give an example:
I am using few lines like that:
this one positions my unit frame next to bartender action bars.
/run local a,b=SUFUnitplayer,BT4Button25 a:ClearAllPoints() a:SetPoint("TOPRIGHT", b, "TOPLEFT", -17, 0)
if there was an addon that does those user defined rules *after* other addons load (so making sure it is trying to move both unit frame and action bars after those are painted on screen) it would be the best thing since sliced bread.