It's a total myth that mangosteen will not survive being transplanted. Actually they are quite hardy. I have shipped bare root mangosteen from Thailand and they all did fine after one week bare root in the mail.
That certainly has been my experience. In all honesty, while there is of course an art to growing plants and to truly being a horticulturalist, I have heard endless claims that plants in general are so delicate that turn out not to be true.
I have been told that my mangosteen would die from transplanting it, that my orchid would die after its first flowers because it is too hard to keep them alive for a full year, that my Birds of Paradise would die from splitting them and replanting them, that my melons would never fruit indoors because it's not enough sun, and on and on and on... and none of these things turned out to be true. I don't know why people are so afraid of plants, and of gardening. They're not little delicate flowers, so to speak, lol! They're hardy machines made specifically to survive against all odds, as long as you can give them the basic tools for life - just like human beings. If you understand that each plant needs a certain amount of water, certain nutrition, certain humidity level, and certain amount of light and oxygen... it's pretty hard to go wrong if you give it to them. Mangosteens in my minimal experience so far don't seem to need much from me - I haven't given it any more care than I have a ficus or a rubber tree, a random houseplant - and yet it grows just the same.
I'm not trying to be arrogant at all. It's just that plants don't need all the fussing from humans in order to grow. They are genetically designed to grow. The problem comes when humans place human expectations on plant achievements. If you don't require a plant to put out the absolute best growth, the best flavor, the most attractive leaves, the fastest fruit, the top of everything... the plant does just fine on its own, no special fertilizers or extra care needed. Grow a plant in an environment in which it is equipped to do well (even if that environment happens to be totally artificial like the indoors in a pot), and it will do what it does, all on its own. It may not have the most stellar fruit without intervention, but I don't care. I like the unique beauty of each plant doing what it was meant to do, in its own way. I love the diversity of watching different plants around me, doing different things at the same time. I love that they do not conform.
There is no particular reason that a mangosteen cannot be transplanted, that it can't be fruited indoors, or that it can't live and fruit outdoors in Florida. As long as it gets the reasonable care that it needs, it should be fine. In Florida, reasonable care involves amending the soil, because it's not likely to be happy on high-PH coral soil, it won't get the nutrients it needs, and will become susceptible to disease - just like a human lacking sufficient nutrients. But just because fruiting mangosteen in Florida hasn't been done a whole lot before, doesn't mean it can't be done. The same for indoor planting. The right soil, the right light, the right temps, the right watering... and it should be fine.
From what I have seen, mangosteen are not delicate, and anyone who wants to should give growing them a try. I hesitated because of all the reputation for being so precious and dainty... but I have treated mine a bit harshly at times and it is still kickin' it. There is no reason to fear - except of course for the price tag of the initial plant - which in my case was around $120. But it already made me pretty close to that much worth of happy, looking at it every day for over a year up close in my house and watching it grow while seemingly never move a muscle. It's a pretty cool, attractive plant.