@bob_veng My explanation for PST-in-EET was much simpler:
A portal to Sigil opens early in BG1, such as near the Friendly Arm Inn. You can find The Nameless One and Morte (likely an inseparable pair) in or near Sigil's mortuary and proceed with the PST story as normal while still being able to return to Faerun via the same Sigil portal. Once the party heads on its interplanar adventure to Ravel's Maze, The Grey Wastes, etc., it can't simply warp back to Sigil/Faerun. That section of PST must be finished before being allowed to return to Sigil as normal.
According to this Christ Avellone interview, Ravel's incarnations coexist within the D&D cosmos having an unconscious connection to each other. Imagine it somewhat like a Wizard who had a simulacrum army or a clone army with some sort of subtle mental link, but without knowing in-depth about their 'master.' PST's ending can fit well within the EET framework: TNO/TTO sends CHARNAME and anyone not from PST back to Sigil where they simply can't return to the Negative Material Plane. Any items in TNO's inventory at the time of this ending would be dumped at the feet of CHARNAME's party or/and put in an easily-accessed place like the Friendly Arm Inn.
If ToB's ending occurs with TNO still in the party, the simpler method is to call the game won and imply that TNO and co escaped the final battle's plane somehow. A more complex method is to turn TNO into the main character, drop CHARNAME's gear in a convenient place for TNO and co to reach (like Athkatla or Saradush) and warp the remaining party members there.
As for lore-based timeline distortions, either ignore them, use TNO's mysterious past to explain that he was some sort of powerful caster who bent time and space, just say that Sigil and the Outlands have experienced time at a different rate than the Sword Coast.
Sigil acts as a hub for EET modders who want to add to the planar cosmology. Being able to travel to Greyhawk/Oerth for ToEE-in-EET would be wonderful as an option regardless of how many ToEE assets were used.