But new technology can not be kept secret forever, eventually, the technology gets out. When something is ready to be invented it will be invented. And it wouldn’t be small one off’s like your example, everyone from the future for ALL of eternity of the future would be traveling back in time as tourists.
Probably not. For one thing we don’t know how much it costs. It might never become anything other than really expensive. Also there’s a lot of people that don’t travel now. Like even a little bit. There are people that never leave their burrow of NY. People in England are notorious for never getting more than 20KM from their town, except for maybe on a party bus that follows their football team. Add in the fact that in any future that could have time machines our present is a 3rd world country, the freaking stone age, how many modern tourists go to stone age villages in middle of nowhere Africa now. I mean would you really want to travel back in time to before antibiotics exist? That version of the world any injury can be life threatening? I’ve got a co-worker that broke his ankle on a trip to a “less civilized” part of the world, it was really rough until he could get back to the states and real medicine. It could happen and just never be cheap or convenient or popular much less all 3.