When I typed this I had it formatted with an easier to read layout which was not preserved when posted. Not sure if I can edit to fix

I would use an outside edge product

https://www.schluter.com/schluter-us/en_US/schluter-us/en_US/Profiles/For-Walls/Edging-&-Outside-Wall-Corners/Schluter®-QUADEC/p/QUADEC?facets=false

Thanks. Trying to avoid as it’s a prominent location and I don’t think it will wear well over the long term.

A few ideas additional considerations. The marble is not available in trim pieces that could work. I have about 3 weeks before tiling starts. I can probably rush trim for the ceramic tile but I’m not certain it will actually solve the issue because there is still the problem of the two materials meeting. It will be $$$$ to add trim. We could abandon the wainscot or we could not add wainscot on the two walls where the materials meet but probably won’t look great.

I think this plan is pretty good. Trust your tile guy (but have him do a sample first). Remember that stone (especially marble) is much easier to cut than tile. It is softer and you don't have to worry about the middle being a different color. It's going to look nice.

I would have ordered the tile trim but I think this is probably better when you have two very different tiles--you don't want too much fussy stuff going on.

Love the tile samples...nobody is going to think twice about your tile interface.

(Schluter is usually kinda ugly.)

Thanks. I debated the trim but it still doesn’t solve for the two materials meeting. As you noted, the marble can be cut, the glazed ceramic cannot. I do have ceramic trim that will exterior from where the wainscot ends up to the ceiling so the unfinished edges of the ceramic do not show.