That's one solution. These old iMacs (called blueberry Macs) are readily available on the Internet sales sites. I have a few of them, with dual-boot drives to boot between different OS versions. I collect vintage machines, and the ones I have are different versions and colors and still work on the Internet although slow. Lighter faster PowerPC systems are still available. There are people out there who can convert almost anything (I can do most except my punched paper tape rolls and 9-track reels from the 70's). Best idea is to plan ahead, and constantly move copies of files to newer digital platforms. No excuse not to do it. DVD's go bad and are becoming obsolete. Same will happen to USB sticks. Important files should have printed counterparts stored in a safe place. If not, too bad.
I have rendered all of the movies to raw video and have stored them on backup and a RAID NAS. All are in uncompressed AVI. As you mention, I will have to migrate them to newer formats and hardware in the future.
Here is a bit of irony. Photos shot 100 years ago have a better chance of survival than a digital photo shot this morning. Low tech or no tech will survive when high tech will not. The late 70s early 80s is when things got more complicated.
I expect AVI and jpeg to be around for a few more years. Maybe I will “print” the most valuable pictures.
Unfortunately, my dad wasn't as careful. How would he have known? The good news is that he printed some of the files.