As time rolls on, fewer and fewer Atari 2600 consoles will be available...
As long as video games are popular, there will be an interest in classic game systems. As time progresses, Atari systems will be cannibalized to fix non-functioning systems. Will people take the time required to upgrade these systems to work on modern TVs? Don't know... it will slowly become a lost art.
There was a time you could go to garage sales and find Atari 2600 game systems by the galore... those days are past. But they are readily available on Ebay for 5-10x what you could pick them up at a garage sale.
As with anything, CONDITION is everything. If you have a nice specimen, you can expect a collector to get excited.