The sandbox mode is already available (endless checkbox in options). Also check out the modding documentation in the 1.0 download. At least some of the tfs you mentioned (multiboob would be possible but a pain, the rest would be a TF tagged potion, see the template) can be implemented using it. I plan to focus on rewriting a lot of the more clumsy lines and polishing the game before adding additional middling quality content myself, and secret characters would be a systemic rewrite of how descriptions currently work (though reworking it to add the ability to mod characters/descriptions is planned for a month or two down the line, v2.0).