shead - I sort wash loads into 4 categories: whites, lights, darks, jeans. On very few days would I want to put everything I'm wearing into the same load. And obviously, lives are different. DH works on a farm. All of his work clothes (which can amount to more than a load per day in the winter when he wears multiple layers) can all be washed together. It will be FAR more convenient to wash his clothes in the master closet and put immediately away than lugging them to the other side of the house and back again to put away. 90% of my things can be washed together as well.

My top item in that category would be a curbless shower. Curbless showers aren't realistic in a remodel. Anyway, the OP doesn't have the necessary space. Even if this weren't true, the OP has already ordered a shower pan, and IF I looked at the right thing, it has a 3 15/16 (might as well say 4") curb. Also, reinforcing the bathroom walls in case you need grab bars Yes, an excellent idea -- but I'd say go ahead and put in the grab bars now /use grab bars for towel rods. It won't take much extra effort, and then it's DONE. ; putting the toilet next to a wall to left or right (i.e. not in the middle of a wall), so you can easily add a grab bar later The toilet's fine where it is. A grab bar can go on the side of the vanity, and the shower can have a wall or a half-wall on the other side of the toilet. Good suggestions on light switches, levers for the sink, etc. Yes, a hand-held shower makes cleaning easier -- true for the body AND the shower itself. Also consider: - Ample niches or shelves in the shower ... put in double what you think you need, and you won't have to deal with bottles on the floor. - A body dryer to eliminate /reduce the need for towels: https://www.tornadobodydryer.com/  - Heated flooring in the bathroom. - Storage at the toilet ... useful for extra toilet paper now and you may need medical supplies at the toilet one day. - Dimable light switches that can serve as night lights. - An outlet behind the toilet since you mentioned a Toto washlet.

Honestly, I look at the layout I drew yesterday. The cabinet is nice for extra storage but I should have kept some of that space for more counter. With a 24" vanity, guests can pretty much just put a tooth brush and toothpaste. Where at the other stuff go: On the toilet seat? On the floor? some little shelves above the toilet would help (but personally I don't like that (I am always afraid that will drop (either in the toilet or on the floor very close to the toilet). Again this is your MIL house, she certainly can have any size of the bathroom she wants but 7'0" is the minimum required to be to code. She could check with her contractor.

are bi-fold doors too 1970's? or just the option when you don't have a master closet?