You'd be hard pressed to find a bigger fan of stone and tile than me, but I have tile directly on slab in my current home, and it is cold, cold, cold. About like standing barefoot in the snow [which I do quite often]. Goes to the very low ground temp here in Montana.

The new house will have tile in the bath because nothing looks as good with such low maintenence requirements. It'll keep the guests from lingering there when others are waiting.

It may be less of a problem in your area, and if you envision these rooms being mostly used in summer, that would figure in as well. Maybe you could have a couple big rugs for winter time...

If you aren't built yet, be sure you get some sort of thermal barrier under the slab. I didn't, and it's my biggest regret [so far].

On a similar thread of my own, someone reccomended Dricore, a subfloor thermal break for basements. Using that, the tile may work fine. I'd use Shlutter Ditra over that. It's a great water barrier and crack suppressant.

Choose a tile that matches your beach to better hide the sand, and a nice dark grout. Also, get some samples, compare them for sliping when wet. A low gloss glaze is better than high gloss, and an unglazed, textured porcelain is better yet. Costs a bit more. Cleft face slate might be the best choice of all.

Here is a link that might be useful: Dricore