Only a guess but if they do extend hours I reckon they would take higher than 4500 because of the reasons you mention. If they took say 8500 and it was a Mil Restriced airspace, then class c applies, with E starting at 8500.
Also another possible problem for E to 4500 is the radar feed for BN centre, unless they get the WLM feed.
I remember that being a stumbling block during the famous 98 class "G" trial. Bn centre sent an enroute ATC down to have a look at the old SURAD to use for DTI and poor buggar nearly had a heart attack and left.