dream eater in place of it to get a bit more top end but the whisperers and eldest reborn have been keeping me covered in the late game so I think dream eater would just slow me down.
i find dream eaters more useful than whisperers. If you already have them, try swapping 2 for 2 whisperers and i bet you wouldnt look back.
Flash + permanent return make a huge difference. Usually whisperer is dropped quickly so its a tie 4 surveil vs life scroll.
I do have them so I'll probably give it a try, but like spectre mentioned I do recall a few instances where doom whisperers' thick ass was relevant. Being able to flash out a dream eater could be useful too since that avoids the "Oh god I want to play a body so I can get a clock on my opponent but I want mana open for counters" problem some.
I did end up cutting one whisper agent and the single duress for 2 fungal infection though, after seeing it in the netdeck and thinking about it. Not completely sold even though getting 2 for 1 against aggro (Especially white weenies) is delicious, but it's another dead card against midrange/control while duress at least is generally useful against everything except green stompy and occasionally golgari/wet golgari. May work on beating the sideboard into better shape and playing BO3 rather than BO1, then infection's way more comfortable.
And no white, Jason! If I added white then I'd be going into esper control territory which is just unforgivable. Dimir jank is slow and relatively controlling but at least the plan isn't to make your opponent draw his 60 card deck one card at a time! I also don't mind the thieves being killed all that much. If they stick, great, if not then they eat some removal that could hit doom whisperers and also give a relatively decent target if eldest reborn resolves and ticks 3 and there aren't planeswalkers or anything available. I also agree on spectre again on quench in this deck, I already have enough stuff to try to dodge with surveils (Removal against control decks, non-removal against aggro, land if I'm already comfortable, etc) that even though it'd be good early on it'd be almost dead later. I do agree a carnarium would be good but I haven't got any and my wildcards are nearly wiped out so I'm just living with it. I do really like soot (Seems to nail nearly everything meta currently) at least.
Edit: First stab at a sideboard is 4x duress (Good for control), 1x fungal infection (Mainboarding two but a third for aggro, especially since I don't have carnarium), 2x disdainful stroke (Good for control again), 2x quench (Does seem much more desirable sideboard, primarily for aggro), 2x murder (Not super pleased with it but it does let me nail legendary fatties for more midrangey stuff), 3x notion rain (Can never see myself playing it mainboard because life's too precious against aggro, but sideboard seems great for control and possibly tolerable for midrange. Even then might not be worth it since I'm playing 4 discovery mainboard), 1x unmoored ego (Only got one but it's nice for sideboarding to knock out Teferi or whatever)
Was mostly leaning toward sideboarding against control/midrange since so many of my mainboard cards are shitty against them in general.
Edit 2: Well first BO3 game with that sideboard was against gates and it went great. First match was a little awkward but soot knocked out rams before they could get too ornery and then counters/whisperer to win even though his hand was going berserk with double summit. Second match was a complete steamroll after sideboarding and removing the anti-aggro shit.