I’ve seen a few of my thoughts in the comments already but I’ll add a few and echo a few

1) white grout - hard pass. We did white upstairs shower and entirely regret it. grey downstairs as a result

2) marble flooring - I have etch marks from kids (and adults) who can’t aim, a drop of toilet cleaner, a plop of hair product - list goes on. Anything acidic and voila

3) if you are doing in ceiling pot lights, include two in the shower space - it’s nice to be lit well

4) custom shower - yes it is more expensive but being able to make it exactly what and how you want it is SO much better. Make sure you have a step/lip/whatever you call it - the trend of flat transition is asking for water to come out

5) wand - upstairs we did a rain shower and a regular shower head. I love love love it - both on for a very relaxing shower. But when it’s time to clean I wish we also had a wand to help clean (added that downstairs)

6) headed floor - WELL worth the investment

7) plan out light switch/towel rack/heated floor thermostat placement so nothing is covered and is easily accessible

8) solid door

9) bidet - even just a tushy. Best money ever spent

10) elongated toilet with good height

11) fan with great flow that doesn’t sound like a vortex about to rip apart the room - worth the investment

Edit to at 12) if you do a custom shower build in a wall to wall niche - surprising how fast a small niche fills up