A fraction of DNA is there to aid in folding and orderly structure. That DNA has generally the same sequence, but it can get duplications and such without causing much trouble, and that does happen. That DNA is important, but it pretty clearly isn't coding for anything.

A lot of the rest is unclear. We COULD collect a lot of junk that caused no problems. It could just collect and do nothing. Useless fragments of ancient viruses etc. That's plausible. Or the same DNA could be somehow important. We might have libraries of inactivated viruses so we can recognize them if they show up again. There are lots and lots of possibilities.

The next 50 years are sure to give us a lot of exciting discoveries if climate change doesn't stop us. (Or nuclear war. That would be sad, to knock ourselves down entirely due to our own inability to solve problems.)