Thanks for your comment. You are definitely right about "forever" not matching reality, which is why I placed it between quotes. In this case, what this means to me is a device that could outlive its creator.

I take your point about lifespan of electronics, however I stick to my guns regarding the word "heirloom". Grandpa's clocks did not last forever either without some maintenance, but still managed to pass through generations with the help of repairing hands. My C64 from way back 1980s still works, and the only thing I ever needed to do is replace a fuse and... treat it nicely.