> I wonder what will happen to all of the digital-only movies and tv shows being made today
Why do you feel digital media can't be preserved?
There are DVD renditions of old media. Cassettes were popular at one time only to be supplanted by newer technologies and it will be the same for current media formats.
To cite an example, I used to listen to cassette music while growing up and was hugely fond of them (Walkman, anybody?) That was then supplanted by digital mp3 players, and now streaming over the internet.
If something is worth preserving, newer technology will make sure it is!
That is just my opinion for you.