So I can't help but think that if there were no cost to doing it, it might have been implemented before now.
This explains the choice for 8 decimals:
Finney, Satoshi, and I discussed how divisible a Bitcoin ought to be. Satoshi had already more or less decided on a 50-coin per block payout with halving every so often to add up to a 21M coin supply. Finney made the point that people should never need any currency division smaller than a US penny, and then somebody (I forget who) consulted some oracle somewhere like maybe Wikipedia and figured out what the entire world's M1 money supply at that time was.
We debated for a while about which measure of money Bitcoin most closely approximated; but M2, M3, and so on are all for debt-based currencies, so I agreed with Finney that M1 was probably the best measure.
21Million, times 10^8 subdivisions, meant that even if the whole word's money supply were replaced by the 21 million bitcoins the smallest unit (we weren't calling them Satoshis yet) would still be worth a bit less than a penny, so no matter what happened -- even if the entire economy of planet earth were measured in Bitcoin -- it would never inconvenience people by being too large a unit for convenience.
Of course this ignores the possibility of micropayments, which could be in-game, on-demand, or pay-per-second. But even if a service would offer to pay a fraction of a cent, they could use their internal calculation system (kinda like LN is doing). For example: if an in-game sword costs $0.001, you can deposit $0.01 and still have $0.009 left.. And since it's less than a penny, even though you can't withdraw it, you wouldn't care.
I don't think I've ever paid anything less than $0.01 though.
A VoIP provider might be a better example: they often charge fractions of a cent per minute, and just take it off your balance. You can't deposit $0.01, but once it's in your balance, you can pay fractions of a cent.
