One kalpa isn't necessarily exactly like the next.
And Talos is Lorkhan.

Here's one: Why did the Dres ally themselves with the Hlaalu against the Indoril? And most surprising of all---in support of Helseth's attempt to eliminate slavery? Lore-wise, the Dres seemed the most deeply entrenched slave society. They bordered Black Marsh and were rooted in the slave-trade, had a heavily agriculturally-based society, and hated the Empire. Why? What was behind this about-face? A mysterious leader? Or do the Dres just hold an incredible grudge against Indoril?

Can we get a bit more context here? I don't remember the Dres allying with the Hlaalu against Indoril (just Dres and Hlaalu rising in prominence while Indoril waned). If you're talking about the late 3rd era, many of the older, classically xenophobic Dres were being replaced by their younger, more cosmopolitan children. It was pretty clear that their old ways would no longer serve them, and they were probably smart enough to realize that priorities needed shifting.

Thanks, Lady Nerevar. Yes, I was speaking about the late Third Era civil war incited by Hlaalu Helseth. I suppose a generation change can explain it, but still... This sort of thing doesn't happen overnight. I suspect House Dres would have fought as much with itself as it would have with Indoril. The old guard wouldn't just bow out to the younger leadership. They've got a lot of wealth invested in plantations and slavery.

I'm still not sure where you're getting civil war. Was that from the Oblivion rumors (which I don't have on hand at the moment)? The PGE3 mentions that the outlawing of slavery was 'bloody,' but I've always read that more as riots and localized resistance than as civil war (which would have been mentioned in its own right). Furthermore, we really don't know what outlawing slavery meant. If its anything like the post American Civil War south, the situation didn't get a whole lot better. The Dres could manage to preserve their economy and plantations through tenant laborers, slaves in everything but name. The fall of the Indoril following the dissolution of the Tribunal also likely benefited them politically and financially, perhaps allowing them to rely less on slave labor. According to the PGE Helseth is also brining back some older Dunmer traditions, which may appeal to the Dres. You've also got to remember that Helseth's wife is of the Dres, which gives them a foothold in the royal house.

Bottom line, I think this is still a really open question; I just wanted to throw it out there to see if it was a bit more concrete in reality.

The following line sums it up:

Don't forget that gods can be shaped by the mythopoeic forces of the mantlers-- so Tosh Raka could be an Akaviri avatar of Akatosh with a grudge against his mirror-brother in Cyrodiil.

Just like Akatosh-as-we-usually-know-him could time-scheme against his mirror-brother of the Nords, Alduin, to keep the present kalpa-- perhaps his favorite-- from being eaten.

Notice all the coulds. - MK

I personally favor the theory that the Maruhkati's mantling during the Dragon Break helped make the Aedra more their modern, human friendly selves, and Martin's sacrifice (and Maruhkati modified Akatosh dying to strengthen the barrier) has swung the pendulum back the other way. I have never quite been a fan of the "belief/believers change everything" model.

Of course, given the current lore, I have no way to concretely prove this. I am afraid it may come down to "pick your favored model" right now.

Some Aedra were already more human friendly, or at least appear to be, such as Kyne.

Yes. Words are something like "House Hlaalu and Dres pick apart the carcass of Indoril" or something.

Maybe. But we put so much emphasis on Man/Mer viewpoints that I feel some compartmentalization between god-versions is necessary. But I'm a big fan of Mortal Mental Stress affecting every divine event from looking up into the sky to seeing the Emperor of the 3rd Empire turn into the god of Time.

I have been giving some thought to a question related to this: It is interesting that Umaril specifically targets the modern worshipers of the Earthbones. His enemy is Pelinal and Cyrodiilic Man, he could go after so many different things. He could try to help topple the Empire, for instance. But he chooses to attack worshipers of dead gods. Could taking them out somehow disrupt/change the fabric of things?

Aedra and Earth Bones are not the same. The Aedra only gave up parts of themselves, but they are still planets floating around (but they are still dead.) The Earth Bones are another word for Ehlnofey and they gave up themselves completely.

The magical beings of Mythic Aurbis live for a long time and have complex narrative lives, creating the patterns of myth. These are spirits made from bits of the immortal polarity. The first of these was Akatosh the Time Dragon, whose formation made it easier for other spirits to structure themselves... finally, the magical beings of Mythic Aurbis told the ultimate story -- that of their own death. For some this was an artistic transfiguration into the concrete, non-magical substance of the world... the magical beings created the races of the mortal Aurbis in their own image, either consciously as artists and craftsmen, or as the fecund rotting matter out of which the mortals sprung forth, or in a variety of other anological senses... The magical beings, then, having died, became the et'Ada. The et'Ada are the things perceived and revered by the mortals as gods, spirits, or geniuses of Aurbis. Through their deaths, these magical beings separated themselves in nature from the other magical beings of the Unnatural realms. - The Myth of Aurbis

The Aedra, our "ancestors", "creators", make up the 8 bones, or spokes of the wheel. So on and so forth. The basic point being, have a key connection to the natural laws of the world.

So I still ask, what was Umaril's intention in attacking their worshipers specifically?

I know of this, elaborate it if you think I am wrong. Gods like Y'ffre and Trinimac/'Tsun, one the first Ehlnofey and a cultural hero, respectively, add more than 8 planets/spokes.

Yes, Aedra gave up their "bones", but they did not give up all of them. The Earthbones did. It's why there is a planet Akatosh but no planet Y'ffre.