100% of the world will use bitcoin and it could cost hundreds of dollars equivalent to move a utxo on the base layer, like take it to the extreme where one sat is worth one of today's dollars. Practically speaking only whales (owning >= 1 whole coin) and layer 3's like fedi's move coin on the base layer to service their lightning nodes. 

 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.