https://www.wowhead.com/guides/shado...s-level-squish
Allied Races will begin at level 10 instead of level 20 and will have their choice to go to any of the 8 existing expansions. They will not be able to visit Exile's Reach.
I found this whilst researching your point here. I find it elucidating. This is from wowhead's collected information from Blizzcon 2019, all of it gathered from interviews with and commentary from various developers. Blizzard took the simplest solution to Allied races and Exile's reach, they simply intend to forbid them from going there and will start them at level 10. Whilst this seems primarily to maintain the higher starting level perk of an Allied race, it also respects the lore of those Allied races in that they cannot escape their origins. A Mag'har Orc always comes from alternate Draenor, a Lightforged Draenei is always lightforged, and a Void Elf is always the outcome of infusing a thalassian elf with void energies.
This is my fundamental point. The core race avatars we play, we simply start up one day as a non-descript member of that race whom we then build into the old god slaying, titan thumping champions of Azeroth they are today. The background for that avatar is entirely up to the player so long as the player character is biologically identical to every member of that race. If someone wished to roleplay a Wildhammer Dwarf today using a Bronzebeard Dwarf, that is a choice that is entirely respectable because the differences between the Wildhammer and the Bronzebeard are cultural, not physical and a believable explanation could be deployed to explain the missing tattoos.
In Shadowlands, they will be given those Wildhammer tattoos and they can personally interpret those tattoos any way they wish, from being a wildhammer fan, to a Wildhammer who lives in Dun Morogh, to having a Wildhammer parent.
Similarly the Troll with the sandfury skin could be an outcast, or could have a sandfury parent, or they could simply have joined the Darkspear tribe to join the Horde. None of those outcomes is wrong because none of them are impossible.
Allied races are different. This is why they start at level 10 and will be blocked from the unified starting experience, not only because it's a reward for unlocking them but because the Allied races have very precise, specific origins. In relation to this topic, a Void Elf must always be a Void Elf. A Void Elf can never be a traditional high elf, because a traditional high elf is incompatible with being blasted by void energies till you turn part ethereal. Even high elf 'like' customisations won't change that.
A Void Elf will always be a Void Elf and can never encompass a traditional high elf exile (i.e one that has never become a Void Elf).