Now that we have finality counters, the next time there needs to be a creature that naturally exiles inherently exiles itself upon death like Gloomshrieker, which do you consider most likely to occur? A) the ability gets written out just the same as it has in the past, B) the creature enters with a finality counter on it, or C) the creature has the keyword "finality" that finality counters retroactively become keyword counters for?

Finality counters are deciduous and will be used where necessary.

are enemy color hate cards not something we're likely to see anymore? talking about cards like Pyroblast, red elemental blast, Deathgrip, Lifeforce, gloom and so on.

We still make enemy color hate cards from time to time. They’re not as powerful as the ones in early Magic and they all have to be effects that are in color.

I recently noticed that Gloomwidow is the first non-blue creature since Nemesis to have "can block only creatures with flying". It got me wondering. Do downside abilities have a color pie, or is it mostly dictated by flavor/mechanics needs?

No, all abilities are assigned places in the color pie. We call the ability you’re talking about “high flying” and it is primary in Blue.

I think you're looking at the Commander hybrid issue the wrong way. Most formats define what cards you can play in a deck by what mana you can use, but Commander purposely defines them by what colors the card IS instead. Hybrid cards are "OR" for mana purposes but they're still "AND" for color purposes -- that's what makes cards like Thistledown Liege, Gloomlance, etc. work. Commander excludes hybrid cards because it purposely cares about color instead of playability.

My problem is that changes the functionality of the card. Only being able to play a black/red hybrid card in a black/red deck negates the entire (okay, most of the) purpose of hybrid.