Here’s the floor plan I’m thinking of

I personally would not be a fan of this. In this type set up, the tub is going to get wet every time you shower. Plus, it looks like cleaning around that tub on at least one side will ever kind of a pain. One of the big advantages of a curbless shower to me is for aging in place, etc. if you put a big step up there, the shower is going to be just as difficult to get in as one with a regular curb.

I guess I don't see why having one giant curb is better than having a traditional one. Same obstacle / trip hazard and similar visual effect. We had a curbless shower put in in our last house (concrete slab). It was wonderful to use, and we received complements from everyone who saw it. What type of subfloor do you have? Installing ours in concrete was surprisingly simple.

Thank you all for your advice. Well, I’m looking at curbless purely from an aesthetic point of view rather than making it accessible. The bath is on the 2nd floor on a wood joist system so accessibility is already restricted. From a visual standpoint I was thinking this might give a more seamless look. On the other hand the “step” of the platform might cut the whole bath into 2 sections. The bathroom has a cathedral ceiling so there is enough vertical height. Phew! I go around in circles in my head trying to think what it will look like!
To me the curb in a traditional shower looks very bulky and “fat” at the edge. And in a frameless glass shower is very visible. Also a curb means you are stepping over it rather than stepping on to something. Most slips happen when your foot lands at the edge of the curb. Thinking this, I felt a “step up” might be at least safer than that.
Thus the dilemma! Thank you so much, let me continue to rethink the whole thing.

Look at using the Wedi Fundo Ligno curbless system. It does not require any floor modification and is a completely waterproof system. We use them on any remodel....worst case you may have to recess the subfloor to be even with the top of the floor joists, but there is not real structural work at all.

Wedi Fundo Ligno

You will end up with a curb. I went through this and if you put in a large shower, the pitch requires it.

Wack idea. Hire someone that knows what they are doing. You’re gonna get red tagged.

Then you have a really big curb, this makes no sense at all.

Tub/shower, wet floor, step down, a slipping accident waiting to happen. Or, dark morning, sleepy, on the way to the shower, a tripping/broken toe waiting to happen.

@Bespoke, I already talked to my contractor for the lowering of subfloor option- he said not possible.
And thank you all for your reactions. I think even if I like it, when I sell, the buyer might have the same ideas. So I think I’ll cancel the idea, tolerate the curb, and go with a regular curbed enclosed shower!!
Thanks again!!

A few more pics though

There are stupid and dangerous and illegal non code compliant pictures all over the internet. Not just Houzz.

And this is why you work with a Pro instead of getting marketers bad ideas and making something even worse.

(also, the first of those three doesn't actually have a change in levels, just a change in flooring material. optical illusion.)

A single step is always a tripping hazard regardless of location.

It really takes a level change of two steps or 14+ inches for humans to pick up horizontal plane changes subconciously and pay attention to the change.

That said I am not recommending two steps, (or any), I am just explaining why a single step is always a problem, bathroom or not.

It's great you have come to a conclusion as to your design. It is however not against code to do a curbless shower. We do them on new construction with the recess designed into the plan. In addition, the Wedi product is approved and code compliant for situations where the structure cannot be changed. We always have a door on to handle and spray. We do a frame door option so there is no curb at all. The adjacent floor area is either backboard or liquid backerboard coated with Aredex 8+9 to completely waterproof the area. Just because these options are not seen on a regular basis doesn't make them an issue with regards to code or use. If someone tries to alter the subfloor structure without the sign off and design of an engineer to do a traditional shower system on an existing house, then yes, they are certainly playing in a no go zone. Not much money to have an engineer specify the floor modifications in most cases and if you are investing on a major bathroom remodel, the few hundred dollars for a quick draft and calculation is generally an insignificant amount to the project.

Actually acm, there is a single level change in pictures 2 and 3 above. Enlarge and see how part of the floor meets the back wall vertically.

I like your idea, in fact I am doing it in a home now - you just might need a little more platform room by the tub for getting in and out.

I am a real estate broker, there are many pretty options like this that I have found on pinterest and Houzz, by very high end design professionals and they look great. Use the Wedi Fundo Ligno on the whole platform..

Sometimes there are reasons for doing this, like making the most of your window and views that you miss out on without the platform, and it does make plumbing and install in an old home much, much easier.

I saved a number of them in this, about 3/4 of the way down in pictures. Dont let these comments turn you away from it it can be done and look fantastic!

https://www.houzz.com/ideabooks/33839431/thumbs/baths-i-like-various-features

I'd love to see what you've decided.

If you want a seamless look for the floor, use a 1” square tile or Penny tile for the shower floor and curb that goes with the larger tile on the rest of the bathroom floor, or use the same tile on floor, curb, and shower floor.

When you can’t dig into the subfloor you can still get a curbless shower without having a step up platform. 1 option is a very slight ramp up to the shower level. Another option is a rubber schluter strip that compresses down when a wheelchair rolls over it.