It would be ideal if the new options are all free. In which case, perhaps Slopes could be an option, but it has to be a separate tile rather than being shared. Reason being that, it would conflict with the way putting blocks work. It should work similarly to the platform blocks.
Also, certain new terrain types would be nice, namely the new ones found in New Super Mario Bros. U (Beach, Jungle and Mountain ala Rock Candy Mines, for example).
Thanks for reading.