Why does Necrodominance set maximum hand size by 5 (setting it to a specific value) rather than decreasing it by 2 (like Thought Nibbler or Locust Miser)?

Different cards will sometimes approach issues in different ways.

Are there effects that Magic used to do that it avoids doing because of digital? One example I was thinking of was something like Mindslaver effects, which seem like a monumental task for digital clients.

First off, read this:

Why I Decided Not to Do Emrakul, and How We Shipped It AnywayDigital more influences how we make cards, doing things like “target opponent” rather than “target player”, but we do have to think through what we’re asking of the digital team for each card we make. Sometimes we will change a card if it’s going to cause major aggravation in digital and there’s another way we can do the effect. Sometimes (see the article above) we do things we know digital will have issues with because we think it would be good for tabletop play.

Regarding Rabiah, here's what I (and I suspect others) want to see: I want to see a Persian/Arabic plane. It does not need any connection to the original Arabian Nights set or story (if there was one), but I would like it to be called Rabiah. And maybe have some clever Time Spiral style call backs (like how Fool's Demise was a reference to False Demise)

Do others agree with this sentiment?

What's a old Magic slang word or phrase (like mill, "go face", fire breathing, etc) that people don't say anymore but you wish would come back?

I kind of miss “mise”. : )

When I look back at the sets when I started playing (around Odyssey) and I think about sets now: It feels like there used to be more vertical cycles (Thought Nibbler/Eater/Devourer) or just cards that were just uncommon upgrades of common cards (Gnat/Locust Miser). Is this my perception or does WotC do fewer obvious rarity upgrades now? I have my thoughts why WotC would do it less, but could you talk about this briefly?

We do less vertical cycles as they structurally do a lot less work than the vertical ones.

Theros would be a great place for a black card like Mire in Misery, or a black card like it, to get into standard. Right?

It would be. : )

Is white's minor new thing going to be similar to mire in misery giving black enchantment removal, where it gets to do something that other colors can do but not as efficient?

It’s nowhere as major as that.

Just saw Mire in Misery, this is the black enchantment removal you've been hinting at right? What is the extent of enchantment removal in black? Is it just edicts?

Here’s what we’re up to. We realized that three different colors could get rid of artifacts (white, red, and green), but only two could get rid of enchantments (white and green). Black seemed like the right choice as it had two permanent types it couldn’t remove. Now, red has trouble with enchantments and black has trouble with artifacts.Our constraints for black were as follows. We definitely want black to be third in efficiency behind white and green. We also didn’t want black to be able to destroy its own enchantments as we like the Deal with the Devil enchantments in black (this was the major reason black hasn’t had enchantment removal). With those constraints, we’ve started designing cards. Our plan is to roll them out slowly, so I don’t believe Throne of Eldraine has one. You will see more though, just slowly.

Golden Demise didn't happen in the actual story. It was a false memory.

Wasn’t the false memory part of the story?

I'm excited about the cohesive creative for Unstable, but I'm worried that it won't leave much room for fourth wall-breaking classics like Look at Me, I'm the DCI; Timmy, Power Gamer; Richard Garfield, PhD; or even Mise. Each of these examples breaks the fourth wall to a varying extent- are we going to get to see the full range? Will we see them in the same quantities as previous Unsets?

There are still some fourth-wall breaking cards, but less than previous Un-sets because we wanted to bring a cohesive world to the set. One of the things we always try to do in Un-sets is make use of modern technology including creative elements.