There you go. You just said it yourself: 500k sats will be dust.
I don’t believe that only whole coiner will be able to transact on-chain. I think 1m sats will always be economically viable. 

 ?? In that hypothetical, 500k sats would be the equivalent of half a million today's dollars 

 You said only whole coiner and L3s will be able to make on-chain txs. That implies that 500k sats are dust.