Not a bad idea at all for the shower floor. It is textured, and has grout so you get a lot of traction then this White marble, Gray Marble and Nero honed pebble mosaic is $9.25 Square Foot and Free Shipping for 2016.
Looking to add to the incredible white look of Venato. This white flat pebble is another great option. $9.25 a Square Foot and Free Shipping thru 2016 (maybe longer but apparently have to put a date on these things).
Pebbles are an excellent and affordable option for a shower floor. It provides grip and traction and feels great underfoot.