As I have heard, TESO will take place around 1000 years before the events in Skyrim because of the "huge" hole in the lore without an emperor. This will then happen between 2E 430(when the last akaviri emperor is assassinated by Morag Tong) and 2E 852(when emperor Cuhlecain comes to power). Around 400 years.

But as written in the first edition of the pocket guide to the empire, the Aldmeri dominion is not founded before 2E 830. And since they are a part of the game, TESO must happen after 2E 830, and before 2E 852.
Then it will be around 700 years before the events in Skyrim, and TESO can only be for maximimum 22 years. Is that really enough time if TESO are here to stay? And if it is like this, TESO can not happen few years after the assassination of the akaviri emperor, like I understood it should be. And the game will happen while Tiber Septim already is born.

In my opinion though, it may be a solution. The lore about the Aldmeri dominion is in the pocket guide to the empire. This book is written by the imperials under Tiber Septim. And of course they had little contact with the elves. Elven books had also been destroyed after Tiber Septims conquest because of many reasons(for example the Alessian order who burned many elven writings).
Because of all this, the imperials must had little information about the Aldmeri dominion. For example they did not know that the khajiit were a part of the dominion.
And then this date( 2E 830) may also be wrong. Then the Aldmeri dominion can be founded earlier, and TESO can happen earlier (as first announced).

Any thoughts, corrections or perhaps answers to this?

You are correct. The PGE date for the first Aldmeri Dominion is most likely wrong. If I remember correctly, in one of the interviews they said the Akaviri invasion of Morrowind was about 50 years ago, which would place TESO at 2E622. Something like that.

Remember the old saying, "History is written by the victors."

One of the first questions about TESO, lorewise, was "why have we never heard about this part in the lore before?"

Well what if Tiber Septim not only ordered the burning of elven book and the writing of revisionist history, but also that all record of the tri-faction war for rule be stricken from all knowledge...

And then there is another possibility which I raised in another thread. That the Nirn of TESO is in fact a parallel world, one of many in fact, taking into account the multiple servers that will exist. If that is the case, the core TES world's history does not include the events of TESO because in that world, they never happened.

I think part of the reason we haven't heard much of any of this before would be a combination of no one in the heartland of the Empire wanting to admit that they got into bed with a necromancer and the Prince of R.ape, and the Dark Ages effect - it was such a confused and conflicted time that reliable records of the period simply don't exist. I mean, the Cyrods wouldn't be in any hurry to admit that they nearly got all of Tamriel dragged into Coldharbour because they were in a bad spot, and neither Cuhlecain nor Tiber would really want to acknowledge that the Empire they were claiming direct descent from was one that had, just a few scant centuries prior, basically turned into an entire nation of daedra cultists.

I imagine in the end it's a combination of poor record-keeping due to the chaotic times and intentional censorship to keep the new Empire looking legitimate. It helps that the three factions are almost universally made up of races who hate each other - they'd have no interest, once things were all said and done, in admitting that they were once actually fighting alongside those other bastards.

This is how I'll imagine it.

It's kinda funny how the series' cosmology brushes gently on quantum theory, even when it comes to the nature of the Elder Scrolls themselves; when used to divine the location or number of other Elder Scrolls, the location and numbers instantly change.