If you use something proprietary, then yeah, it might be difficult. But that doesn't stop us from asking whether something we're interested in using now uses data formats that would be easily readable in 20-30 years.
Actually... I reference a lot of notes from at least 20 years ago. There is a lot that doesn't change, you forget, and is an instantaneous search away. I don't foresee this changing in the interim 10 years.
But even if I it wasn't I don't like to think about the lifetime of any thought as I note it down. This os a distraction I don't need. If the closet with the notes in it fails, I want to be able to read them still.