Ditto! I hope this is either possible or high on the roadmap.

It's actually possible with AttachCell. Try:

FrontEndExecute@
 FrontEnd`AttachCell[
  EvaluationNotebook[],
  Cell["asdasdas", "DockedCell",
   CellFrame -> {{0, 0}, {0, 1}},
   CellSize -> {Scaled[1], Automatic},
   Background -> GrayLevel[.98]
   ],
  {0, {Left, Bottom}},
  {Left, Bottom},
  "ClosingActions" -> {}
  ]

That will persist until you close the notebook

@b3m2a1 you are my hero, that was insanely obscure and super awesome! For years I have wanted to use DockedCells at the botton of my notebooks, this is so cool! I guess it should come with the disclaimer of all undocumented things, which is that it can change without notice since it is not designed for external reliability... but who cares, this is going to be such fun to play with!