Thin veneer concrete is quite brittle. Comcrete is great in compression, but quite weak in tension, so any flexing can easily cause it to crack.

Concrete is also porous.

The down side is that concrete can be made stronger by using a richer mix, and it can be made less porous by the same and by using certain troweling techniques. But those things will give you a hard polished surface, which can be slippery.

Portland cement actually isn't terribly eco-friendly. At least not in my opinion. A lot of energy goes into making portland cement.

The following is not a pure correlation, but just go along with the theme for a bit:

Concrete without stone agregate is essentially mortar. Mortar with modifiers to increase it's strength is essentially thinset. Thinset with pigment for color and bio-additives for anti-mildew capabilities is essentially grout.

Read a few threads and you'll read about people wanting to use large format tiles in their showers to minimize the hassle of having too much grout. A shower with a veneer of cement is essentially a shower of 100% grout.

It can be done, it has been done, but it has to be a thought-through process.

Mongo