There are many different directions to take Delver. You can play it as a more spell-based controlling deck or you can play it more like UR(x) hatebears, with or without burn.
For example, in straight UR you can play cards like Harsh Mentor, Eidolon, or Scab-Clan Berserker. These effects play nice with burn and Price of Progress for quickly closing out the game.
In the past I have splashed white to play Stony Silence, Containment Priest, and other nonsense http://mtgtop8.com/event?e=12172&d=269857&f=VI while that deck later got eclipsed by UWr Mentor, it may be viable post restriction (or maybe not, as the Gush restriction really hurts the deck)
There are also reasons to splash green or black and builds for those but I'll leave those as an exercise for the reader.
One reason to not play Delver is that Walking Ballista basically owns most of your threat suite (Delver/YP especially). Between that and the prevalence of Outcome decks I think all Delver decks need to seriously look at Null Rod/Stony in their builds.