Why is the layout "a pain?" I think that this is a good layout. If this is your only bathroom I would suggest when you remodel hanging a door to seperate bath/loo area from the sink area. That way somebody can have a bath or be using the toilet in privacy whilst the other person is having a wash, cleaning teeth etc. It may be a small space but the potential is huge - you could really transform and define each area with clever lighting.

An alternative to the long tray idea (which would be great and incidentally our old shower tray was only 760 depth and it felt plenty big enough because it was long. I would have it set into the alcoves and walk in at the door side though. ) is to put your wash basin where your olds shower was because the sliding door opening on the shower curve shouldn’t touch it or expose it. So that would give you all the floor space between the WC and the left side.

It's a bit of horrible shape, but do'able. You can just about increase the size of the shower to an offset quadrant at 1200mm x 800mm ( surprisingly room ). You just have to be aware that you need a vanity that's not too deep. I base this on some of the ones you can get from Soak.com at 600mm wide and 395mm deep. The less deep the vanity the more walk room you get across that corner. Ideally you would have a metre, but you get a good 80cm ( sufficient ). The window i made 800mm. It's the placed across that wall 950mm behind the shower and 750mm from the bath wall . I also put a little dwarf wall / shelf at the end of the bath for products whilst using the bath and then the towel radiator is above that.

His preferred layout looks like they forgot to put a toilet in, and to squeeze one in afterwards. We asked the builder to put 2 basins in our new build ensuite. Complete waste of space. There might be room for 2 basins, but there isn't room for 2 people! We have just redone the ensuite with a single basin and the room looks so much bigger