I have built two curbless showers with in the past year and a half. Both where built using Ditra, Kerdi and Red Guard. I have been having more and more clients ask for trench style drains and have spend about 8 months researching these beauties. Quick Drain USA has a nice channel (trench) drain with excellent tech help and a wonderful website. ACO now imports to North America from the UK and I have found that their drain can fit on top of a Schulter drain rough in (this can not be done without modifying the stock unit and I'm sure it will void any warranty). All that said I should have much more answers to this specific question in roughly 3 months time. The more I look at the trench drains and the more we explore the options it creates it's no wonder the channel drain is the hottest look of any new shower. As far a a nice clean looking curbless shower with a simple Kerdi Drain the entire bathroom needs to be waterproofed. Toilets should not be placed too close to the shower entry because a typical floor mount toilet is the biggest weak link in a wetroom floor. A better option is installing a wall mount toilet or small covered curb (i.e. pony wall, glass block wall, frameless glass on low curb) that separates the toilet location from the wet zone. Make sure you pipe your new curbless with at least a 2" drain line (with properly sized vent line) your design and polumbing package might need a 3" drain line so even though you want the new channel drain you may need to install a standard drain in addition to the floor drain. It's hard to teach an old dog new tricks - Push your builder or tile guy to research harder. Be prepared for extra costs. Framing changes, concrete work and structural engineers may need to be used. I designed my last two around standard framing and raised the transition from the hallway to the bathroom to 3/4" - 1" (Solid hardwood reducer at doorway) and pitched everything back to a single Kerdi drain.

You might want to also take a look at Zurn floor drains. My showers all have Zurn FD-2290-ST drains which are square, rather than round. They're commercial grade products, but I think the square shape works better with square floor tiles and provides a more architectural look. They're available in several sizes and finishes. Here is a link that might be useful: Zurn Floor Drains

The only real thing that matters in my view is the slope to get the water out of the pan. The drain needs to be at the lowest point. You still want to be able to stand on the surface without risk of slipping into the lowest point. So the slope can't be too shallow or too steep. If you want to put the drain someplace against the far wall I don't see why there could be an issue, except as Ieffablespace mentions, the efficiency and cost of plumbing more run. In my remodel all my joist were in place. I had to plan carefully were all drains and water sources entered into the room. There were a few places where I had less than an inch tolerance to one side. If I couldn't make it work one way I had to go back to the drawing board. I did my own layout plans. I knew all my dimensions of fixtures. I consulted my plumber often. It is a team effort.

The only way I can see to do this is to raise the floor on the new shower to allow the extra pipe a one-quarter inch slope per foot. This is both the standard practice all around the country and the minimum slope allowed by most city/county/state codes. I wouldn't think it would make too much of a step up, however I'd check the local codes before doing so. Most inspectors are happy to help you do the job right the first time.