What do you guys think

[beanz]

I always thought it was a 10 metre run!?! Either way, you know the customer is going to balk at the threshold strips. Maybe just try for matching Silicon joints in the doorways, although that may not be possible, due to laying out.. The other option is that you could explain the potential problems, of tiling right through, and just go with what they decide. I've done it a few times, and so far, been lucky.

 

[beanz]

As you're going to Ditra the floor anyway, I wouldn't bother with cement boards. I'd just ply it with 12mm ply, screwed every 150mm. Unless height is an issue? Let the builder ply it, then show the customer that its not flat, and you'll have to level it with SLC, before the matting can go down.