Moving to Elite/Ultimate Difficulty Without Restarting The Base Game

I assume you have played since 1.2.0.0, and so your feedback is taking into account all difficulties at least scaling (in most areas) up to level 100?

If so, best practice is currently to unlock the ability to buy Merits, and just start a new playthrough from level 1 on either Elite or Ultimate and do as much of the game as you want there. I get that it is more awkward to arrange for a multiplayer group where not everyone is in the same place or able to jump through the hoops, but it is relatively easy / doable / a workaround.

Three times through for three difficulties is the classic setup throughout the ancient past, and I get that it may look as weird to PoE players as PoE’s mid-game difficulty jumps did to me the first time. At least being able to start a new character on Elite or Ultimate (which can be tricky!) is a workaround or kludge for what you’re looking for.