Shouldn't mechanics that spawn naturally be also visible on "extra content" panel?..

Be it abyss, mirror of delirium, breach or whatever.
It's not necessary by any means. Nothing is if you think about it.
But it would be nice to have.

I think that ESSENCE needs to show up on map, now that we do not have monster icons it is hard to farm it.

A map is only finished when you've cleared every piece of content that spawned on it.

Every league mechanic, every rare, every strongbox, every wisp, essence, summoning, heck even every blue/yellow chest.
To leave the map and go to the next one without clearing everything that spawned is wasteful.

So yea, everything that exists in the map should be shown, either on the minimap or just on the quest tracker "extra content" section.
We shouldn't be missing things because we didn't even know it spawned, and we shouldn't have to tediously fill in every spec of the map to ensure nothing was missed.