Without a shower pan, how would you keep moisture out of the walls? Water does wick, sometimes a long distance, especially on the horizontal, but even more than you think vertically, too.
While not using a liner seems to be used in some places, it does not meet the building code. Depends on exactly where you live as to what code applies. National codes require a waterproof liner, sloped a minimum of 1/4"/foot to the drain. Typically, it must also go up the walls a minimum of 2" above the top of the curb before you can install any fasteners. Since you aren't planning a curb, that can create some issues with the inspector, too, but is possible with the proper design. Neither concrete nor tile is considered a waterproofing layer...moisture WILL get behind/underneath/in them. It needs a sloped waterproof layer to direct that accumulated water to the drain, otherwise, it will just accumulate. Texas is prime country for carpenter ants and termites...not having a proper liner will attract them to your home!
It's not the easiest thing to produce a nicely sloped concrete pour...it tends to run, so, trying to make the whole thing look like a slab can be problematic.
What you are describing is a wet room, where the entire room is designed to drain and thus needs to be waterproof. You do need something to keep water from running out into the hallways...might be enough, if the room is large, to just have the slope and the drain far enough away from the doorway.