That thought did cross my mind. It'll surely depend some on the frame though, and ironically I bet it'll be the super high-end frames where every possible gram has been shaved off that'll go first. Steel or aluminum, though? There's no reason those shouldn't last 100 years with even halfhearted care.

Any bike worth buying can be BIFL if you take care of it, that's one of the wonderful things about bikes! I do get why people are into Rivendell, though. For a particular cycling philosophy and aesthetic, they are really just the ultimate.

…that counts as a joke?

Came here just to say this. The cloudy white ones with the blue caps that look like actual labware and not a spinoff from a company that originally made labware, are functionally indestructible. If you think they're ugly, put some stickers on them. If you're worried about the health effects from drinking out of plastic, take a moment to think about what most if your food and water already is packaged in/flows through, and stop worrying.