In our new house hubby poured thin layer of concrete over existing slab in ensuite and main bathroom, embedding coloured stones in it. It's been polished and sealed with crushed glass added just to the shower area .... we definitely won't slip on it, but will have to use a soft broom to clean shower area, as it would shred the pad on my mop (we haven't moved in yet).

Terrazzo. You may be able to find full one at a demo yard.

They are probably concerned that silicon becomes mouldy. If you are happy to resilicone every 8-10 years it shouldn't be a problem. My main concern would be the very slippery surface you would be creating which may be a safety problem.

You'd have to get expert advice I think they'd have to prepare the floor before laying concrete from what I have heard it is pretty hardy stuff these days and looks wise it's great, as I am no expert you'd have to get a licensed concreter to give you an opinion if it is feasible, as I said it doesn't have grout and as a woman myself keeping grout looking pristine is a full time job and a PIA! I have to agree with you on that one.