D&D 5E Etherealness, Deep Ethereal, and Plane Shift.

[SkidAce]

So final version...

Based on past play precedent, and several rules references from 5E and older guidebooks;

Etherealness: You remain in the Border Ethereal for the duration (8 hours) or until you use your action to dismiss the spell. (House Rule: or action into Deep)
Oil of Etherealness: as Etherealness, duration 1 hour.
Plate Armor of Etherealness: as Etherealness, duration 10 minutes.

it appears to me that when in the Border, unless magic is sustaining your presence, you drop out onto the material.

So I will use Etherealness as is, with house rule action into Deep, and use Ethereal Jaunt to go directly to Deep (random location).

In either case, when traveling the Deep, and finding a specific color curtain, for your world or another, once you step into it, be ready to "materialize" through the Border and onto that world, no longer ethereal.

I might give you a round when traveling through a curtain to see and back out from certain danger, such as a sea of lava or something. Might not, better cast protection from fire BEFORE enter a curtain you think leads to the Elemental Plane of Fire. I will develop idea later.

If anyone wants revised pics of my spells let me know.

 

[Sword of Spirit]

it appears to me that when in the Border, unless magic is sustaining your presence, you drop out onto the material.

What's actually going on there is all of those are magical ways of getting into the Border Ethereal, which also bring you back when they end. It's not that you can just move into the Material Plane (or an Inner Plane) at-will from the Border Ethereal, rather it's that those spells and items normally used to get there produce an ongoing magical effect on you for their duration that provides you a return ticket. If you use an instantaneous spell like plane shift or gate to get there, you're stuck unless you cast them again to get back out. At least, that's how it's worked in all previous editions, and I don't see anything to indicate that you can just choose to "drop out" of the Border Ethereal in 5e.