It's something we'll take in consideration. The way we're looking at it is if a mechanic is impossible without being able to teleport away, it should be changed for both Ruthless and the core game.

Items that grant movement skills are currently still obtainable, but the skills they grant will have longer cooldowns. We'll be keeping an eye on this in the lead up to the 3.20 expansion and may modify them if needed.

Yes.

Yes, unless you've also selected Solo Self-found.

Challenges will be disabled for 3.20 because some may not be completable in Ruthless (for example, some content might be disabled while we continue to work on it, but ideally we will have everything in that we intend to be part of Ruthless). We'll try to sort out some solution for challenges in Ruthless from 3.21 onwards.

No. Ruthless is additional content coming out alongside the 3.20 expansion.

No. Due to the scarcity of item drops in Ruthless, a default item filter is unlikely to be necessary.

No. Balance changes made to Ruthless have no bearing on the main game. If we feel a change is good for the main game, we'll just make it there as well.

We currently plan to have the option to make Ruthless private leagues for the 3.20 expansion.

The intention is that all past leagues will be available, but some appear in different forms. Content from past leagues is encountered less often than in regular Path of Exile.

Yes.

We don't currently have any new achievements planned specifically for Ruthless.