I'm not sure DE would work to well anyway.
New entrant offered ATC, could choose SNCO or Zob entry levels. Why deliberately cripple yourself entering at SNCO when you could commission?(bearing in mind none of them have any idea really what they would be getting into).
Plus, Towers full of SNEC's and Zobs who have no-one in who has been in longer than a couple of years? (Especially all those long boring out of hours times, weekend, night shifts etc) Ouch.
Also, consider the fact that these DE's would most likely end up being 1st RO for the guys in the tower, having no idea of the content of their duties. Completely unable to advise the 2nd RO on any aspect of their write ups.
Bag of w@nk in my mind.
It would happen.