Meaningful quantum computers are a long way away, and we do not need to start building quantum proof bitcoin just yet, but I don't think they are 500 years away.

Even if everyone was using second or third layer solutions rather than the base chain, you still need to use the base chain to enter those layers. With Lightning as it stands now, even just to get everyone in the world to open a single channel would provide decades of on chain transactions and fees for miners. But with things like taproot and channel factories, that becomes more efficient. What other layer 2 or 3 solutions will we have in 100 years? And then there are things like merged mining, which already happens. We simply have no idea what the ecosystem will look like in 100 years.

As pooya87 points out, taking coins which haven't moved in x number of years gives rapidly diminishing returns. You'll get millions in the first year which will cause absolute havoc for miners trying to reorg the chain to claim the rewards themselves, and then that will rapidly fall off and you'll be left in the situation you were in before.