Generally, it's a really bad idea. Hardwood flooring is typically not a suitable substrate for tile installation, since it's surprisingly unstable, as in, it moves a huge amount based on everything from humidity, temperature, foot traffic, etc.. Sanding it down, and tiling directly over it will be nothing but a disaster. Substrates for tile do two things. they provide stiffness, so the tile and the grout do not crack as the floor flexes, and they provide a "decoupling" membrane, that isolates the movement of the subfloor from telegraphing through the tile. For example, a plywood subfloor in a new home can shrink to the point that joints that were originally tight can open up to 1/8 to 3/16th gaps. In a proper tile install, this subfloor gets another layer of material, such as 1/2" cement board, Hardie board, or even a high grade 1/2" plywood. This material is installed so that the joints are offset from the subfloor joints below. Once installed, it stiffens the floor to prevent flex and it "decouples" the subfloor movement from the tile. I have seen a job where a DIYer tiled directly over a single layer layer of subfloor in a new home. After a few months there were interesting lines where the floor cracked directly over every joint in the subfloor.
In your case, I would look at all available options that would give you the look you want, without a true tile installation. If you can't find an acceptable option, I would look to the John Bridge forum, and be sure that your whatever direction you head is within industry best practices, and according to manufacturer's instructions. In other words, don't end up asking the question, getting ten answers from seasons pros. who say, "I wouldn't, and I would refuse the job if the customer won't agree to removing the hardwood, and installing a proper subfloor", and one from some guy that says "no worries, just staple a layer of 1/4" plywood down and have at it", and give much weight to that answer. That guy is the one that's best ignored. Good luck.
