Foss alternatives generally handle this by either not changing the format too much or by making old versions available to download in perpetuity and then you can manually upgrade your decades old library at your leisure. I'm really glad they don't spend their already limited resources on trying to handle every possible old library file under the sun, as long as you've got incremental upgrades working you've got a path. And if you are not using it on timescales that would allow for incremental upgrades you are not the ICP anyway so they've made a good engineering decision.
Right, but do these incremental upgrades preserve the look of the image? Or do they just keep the library accessible?
For example, increasing exposure in poorly lit adds noise, so you might counteract with a noise removal filter. Later on, the developers come up with a better exposure boosting algorithms that takes more sensor characteristics into account, and produces less noise.
Ideally, you’ll get this new algorithm on all new photos, but not the old ones. It’s unreasonable to expect you to go through all images you already processed and decrease the effects of the noise removal filters.
Or maybe you liked the noise on those pictures, and now it’s gone, and you need to add it back.
It’s a very reasonable to expect your photos to look the same long term.