Predicting anything 50-years down the road is next to impossible. There will certainly be be booms, downs and all other mater of things socially, economically, and globally in general. How these will effect the retro game market cannot be seen, however I do believe hat despite all of this, retro gaming will crash relatively soon. Probably within the next decade.
What were are seeing right now is the coming of age of people who grew up during the mid to late 80s; they are getting careers and disposable income, and most also happen to be in that sweet spot between single and no kids and married with children. They are going back and collecting relics from their childhood which has increased demand on older games. However this same thing happened a little over a decade with Atari games as people who grew up during the 70s were in thee same position, which caused that niche to explode as well. Admittedly it was not as big as NES, SNES, or TG16 collecting is now but prices were a ot higher on Atari games during the mid 90s up until the mid 2000s. Now Atari games can be found everywhere and even some of the rarer titles are a lot cheaper than they were. This same spike in collectibility and price has happened in other hobbies as well including toys, baseball cards, and comics (which are coming back again). All limited comodities that rose in price and eventually plummeted after years of being in demand.
What will bring an end to the retro gaming boom has already begun. People lose interest, people take on all kinds of new responsibilities (mortgage, kids, medical bills) and sell off their collection, once again increasing quantity and decreasing price. This will happen more and more over the next 5-years and I can't see any retro games, outside of the very rare titles retaining their value. Even games like Little Samson or Ducktales 2 will decrease in price. Probably never to their pre-retro gaming boom prices, but at least half of what they go for now.
Again, this has happened with most collectables over the years and I have no reason to believe retro games are an exception.