Would it be all machine or human accesible?
How about a bit of both?
If we're talking about totally out of the box here, then my ideal tickling machine would be a female android with a wide variety of sensors and other unique attachments and skills. Off the top of my head, she would have retractable/extending nails, built in under the skin viberators in her finger tips, hands, tongue, lips, toes, feet, and probably several other fun places, various parts of her body would have area's that could open up to allow metallic tentacles to extend from the bottle for further tickling. The tentacles themselves would likely have a variety of other attachments, like brushes and feathers for tickling.
Her internal sensors would allow her to tell exactly how far she needed to push a person for any reaction, be it orgasm, passing out, loss of bladder control, etc. She would also have a variety of verble/behavioural settings. One time she could be the silent sadist, not saying a thing as she watches over you, tickling you until you would be screaming for mercy if you could get enough air in your aching lungs to do it, a slight smirk on her evil face. Other times she could be cuddling with you giggling allong as she gently and playfully tickled and teased you, cooing with excitement in your ear.
Physically, she would be alterable. The pigment of her skin, fullyness of her body demensions, eye and hair colour would be totally customizable. Height would be a little tricker, but longer limbs/torso could be purchased. One could also purchase additional attachments, like devil tails, cat ears, angel wings, etc.
And that, roughly, would be my ultimate tickling machine.