there are many options how a Delver deck can look like but unlike other decks it is often usually a predator deck of some kind even though it has often more linear plan than other decks. You can either go for a very streamlined version or more fluid version that can play a control role. Splashing black usually makes you more control than then tempo.
The creature suite is not really that given. While you will most likely play 4 Delver of Secrets (it's usually 4 or 0), 4 Pyromancers doesn't need to be the case. I was often boarding out 1-2 Young Pyromancers in many games and it is to be seen if that might not be happening now as well. Note that without Gush this creature is kind of worse. So it depends on how many spells you can put in the deck and meaningfully use them.
Snapcaster Mage becomes very playable now but in order to get the most value out of this deck I'd still stick to a certain number of JVP. Since the deck is not that fast though now, maybe running Snapcaster Mage may be correct. I doubt it though. (so far I just board them out almost all the time...). I put Snapcaster Mages in because I want to have around 10 creatures that can swing. So if I won't find a better replacement I'll stick with this card.
The engine should be restricted spells + Preordain. You will need more though than just this and it is still to be seen what it may be. So far I tried all kind of tutors instead because I couldn't find anything better. The best card is actually Night's Whisper but is black which also a slightly different approach to how to play the deck. The cards I play now are 2 Spell Pierce, 1 Pyroblast, 1 Fragmentize, 1 Merchant Scroll, 1 Mystical Tutor. I'm still undecided about the two tutors. The other cards are doing their job well.
I wouldn't think Dack Fayden is necessary. At least not now before the metagame settles. It wasn't usually good even before. If you want a three drop Snapcaster Mage is better.
Mana Denial should feature Null Rod effect. Wasteland is a question. During the Shops/Mentor era it was actually good to play 4 Wastelands since that helped a lot, not only against Shops but also against other decks and even Mentor (if it wasn't the UW version). Some versions were very light on lands though so hitting occasional Tundra was good enough to win the game sooner.
Main deck hate is about to be seen. I'd run an enchantment/artifact hate main deck, otherwise I wouldn't bother. But a card like Smash to Smithereens might be ok though since it can deal 3 damage...(I run Fragmentize, but wouldn't run let's say Shatter....um or well a good artifact removal in those colors...that is)
As for Wasteland, if you play that as additional lands (spell slot) it is ok. Otherwise it can really put you behind. I tried to avoid running Wasteland as much as I could because I always needed every single blue mana I could produce to play cantrips and cheap countermagic. Wasteland was always messing with that plan. When the metagame changed a lot, wastelands became more of a necessity (see walking ballista and lands like workshop). I wouldn't say that wasteland is bad and I wouldn't say that wasteland is good either. It will depend on the decks that will emerge. By default I'd rather play without the card in my deck and I have 15ish lands available to me with a single strip mine being the additional land (15th land).
The same goes to Harsh Mentor, this card in diverse metagame is not good. Against some decks you need 4, against many you'd rather see anything else than a 2/2 that occasionally hits an opponent for 2 (fetchland usually). I did not think about how the deck should look like now though, so not sure what I'd play instead. Most probably some combination of JVP and Snapcaster Mage (I feel 1 would be the right number). I started with 3 Snapcaster Mages and that's certainly a number you don't want to run. Anyway Snappy is better than Harsh Mentor.
I play white because I expect Oath decks to be played so I rather have my Containment Priests ready (RIP and Stony Silence that is more difficult to get rid of...). Also play PTE to deal with some things like Blightsteel Colossus or Marit Lage.
Just build the deck and play with it. There are several different approaches but I would fall back on the Delver decks from when P9C started.
(By the way Abrade performed better than I expected, I like it more than Smash to Smithereens, but my deck was rather build against Shops by default)
I'm currently trying this. From there I will try to tweak it to suit my needs and the metagame.