While as a Ph.D. Chemist I am quite interested in different coating to improve a fretless neck, I remain most enthusiastic about the possibility of using a ridiculously hard (and currently fairly cheap) wood to make the fretboard. I am speaking of Ipe (Tabebuia serratifolia), sometimes known as Brazilian Walnut.
Ipe is the king of the JANKA scale (which measures the pounds of force needed to push an 11.28mm ball bearing half way into the board) at a whopping 3680 lbs Granted this is a bit subjective but Ipe is easily 2.5 times harder than "hardrock" maple (Acer saccharum), and its commonly used for decks (until they empty the Rainforest). While its a bit green/brown it stains and polishes well and I've even found some nice figured pieces in a pile of decking. Get ready to use a TON of sandpaper and elbow grease to radius sand it, its a bit like sanding marble...