I got my RTT almost 10 years ago. The company who made it went out of business 5 odd years ago. I have enjoyed it but there are a few drawbacks. When I would go to an event or a camp ground, I was the only one. People would come over and ask about it. When they heard how much they cost, people would back off and be happy with their tent. I like being off the ground and not having to look for a flat spot to pitch a tent.
Right now "Overlanding" has become a fad. Your not cool without an RTT or an Adventure Trailer. I'm amazed with the number of mall crawl "overlanding" rigs I see. In 10 years it will be a different fad. The people who were part of the fad will have moved on. The few of us remaining will still have our RTT's and Adventure Trailers. Will people still make gear for us? Of course. Before I had access to all this recent specialty gear, I just used my back pack gear and my camping gear.
Will they still be around in 10 years? Yes but, fewer companies, fewer people running around with one on top of the family truckster never to be used. People will look to us and say, wow I remember when everyone had one.