Our current MBR is close to your first plan, just a bit longer. We have a 5' x 14' master bath with a pocket door between the toilet/shower room and the double vanity, and our ceiling is only 7' 6". We plan to redo the room (it's 1970s era) and remove the wall and pocket door between the "wet" room and vanity because it feels totally cramped. Our entry door is also pocket but is placed more like your second plan, so it limits how we can use the long wall. Have thought about something similar to Plan Two but have almost totally nixed the idea due to the reduction in size of the shower by almost 9 inches from its max potential. Our current shower is 48x30 and it feels cramped to me, which is also attributed to its dropped ceiling - I call it "the coffin." We have no windows in there, and that also makes it feel crowded. We want to do a "tub in shower" idea like the picture someone posted, so we can squeeze a separate tub and shower into the space, but will be compromising by losing the "toilet room" and taking our vanity from 8' to closer to 5'. Our closet is also accessed through the bathroom (door is placed like in Plan One, so we are actually dealing with two doors in our bath - three if you count the existing wet room door), and we have waffled for two years about the necessity of a separate "toilet room" to preserve access for the other person to use the vanity and the closet if someone is in the toilet. Frankly, we have decided that if one is using the toilet, the likelihood of the other trying to use the room at all is very low. We have two other bathrooms in the house and if one of us is using the shower and getting ready, the other would go on to one of the other baths to have privacy to use the toilet, and not depend on a pocket door! That's the reason we think we will nix a pony wall for "privacy" around the toilet, too. Our previous 1950s house had a toilet just next to the vanity and we never used the toilet at the same time as the other person was using the bath (again, we had a half bath as well so could use it if needed) so it's just eating up floor space and visually closing off a tiny room. We are going to have to move our toilet about 3 feet directly adjacent (joists are running in our favor so that is a small consolation) and possibly rerun some H&A ductwork in our dropped shower ceiling (yes, dropped lower than 7'6" - our house was constructed for very short people, I think!). Would love to see what you come up with as we are still in the savings mode to do this project. One other consideration is placing plumbing on the exterior wall if you are in a cold climate. 2/3 of our bath is piped through the exterior wall and I wish it wasn't because we have to be really careful during cold snaps to remember to drip the faucets. You can't "drip" a toilet, though, so I worry!

Solar tube to bring in natural light rather than a window? I don't think there is anywhere else to put the shower that size with that size bathroom. You could also try a clerestory window above the shower/linen closet.

What is the purpose of the "vanity desk?" Does someone like to sit down to shave or apply makeup/do hair? Seems like wasted space when you have a large two-sink vanity already. You could put a linen closet in, instead, which will give you more storage if you don't need or want a huge shower. In the plan(s) further above, with the shower taking up that entire wall, you have *plenty* of room to get out of the shower, towel off and get undressed and dressed. Floor space, a space to hang a towel and lay or hang clothing is all you need - you don't need designated shower-prep-only space.

Without seeing a floor plan I'm not sure what you're thinking of, but you may not have room for two vanities across from each other if they're going to be on the long wall. They will take up two feet each. If the total width is 7 feet, that leaves you with a 36" walkway which is a minimum. If two people are standing at each vanity at the same time you will be bumping into each other. Also, when you say 7 feet, is that inside the walls width, or is that going to shrink once the drywall is up?