Well, that's an easily-achievable dream! Lionfish are extremely sturdy fish, as long as they're not fed a steady diet of goldfish. Get one that's adapted to frozen foods, and you'll have it a good, long time. Extremely disease-resistant, tolerant of imperfect water conditions, and undeniably interesting. People have even used them to "cycle" a tank, although I wouldn't go that far. Rather poisonous, of course.
They don't need a very big tank for the size fish they are, preferring to hover rather than pace. There are dwarf varieties, also.