bug#70664: 29.3; vtable-insert-object cannot insert at top of table

[Adam Porter]

To be clear, I don't plan to work on this anytime soon.  :)

Having said that, using a special value for AFTER-OBJECT to insert first 
would probably be a good idea, because it seems like it should be 
possible to do that, and it wouldn't require changing the signature.

Beyond that, IMHO it might be good to write a function with a different 
signature that would allow more flexibility, e.g.

(cl-defun vtable-add (object table &key after before at)
  "Add OBJECT to TABLE at specified position.
AFTER may be an object after which to insert it; or BEFORE may be an 
object before which to insert it; or AT may be an integer position at 
which to insert the object, 0 meaning first and -1 meaning last (only 
one of these three arguments should be given).")

Then the old function could be deprecated.