Now, we have just <21,000,000,000 mBTC that will potentially be available.
Not sure which prior post you're referring to, but all of these proposed changes are technically feasible (if critical mass of term-usage is achieved). No matter what units are chosen for human use, interfaces, and integration with other systems – the core protocol/system always works on integral satoshis. All of the following tallies are identical, and represented the same in the binary protocol and canonical data structures:
21 million BTCWorking up from a zib=µBTC unit instead, again all these can be used interchangably without really changing the atomic units of the system:
= 21 billion mBTC/"millibitcoin"
= 21 trillion µBTC/"microbitcoin"
= 210 trillion satoshis
210 trillion satoshis/cZBC/"centizib"/"cents"For completeness, you can also think about units that exist but are so large they'd rarely be useful...
= 21 trillion ZBC/"zib" (aka µBTC)
= 21 billion kZBC/kƵ/"kilozib" (aka mBTC)
= 21 million MZBC/MƵ/"megazib" (aka BTC)
210 trillion satoshis...as in, "Some estimate that Satoshi himself may own around 1 megabitcoin (1 MBTC)", or "Mt. Gox misplaced 850 kilobitcoin (850 kBTC)".
= 21 thousand GZBC/GƵ/"gigazib" (aka kBTC/"kilobitcoin")
= 21 TZBC/TƵ/"terazib" (aka MBTC/"megabitcoin")
Since people easily understand large numbers, especially when rarely used, it's far more likely to emphasize the unique size of these numbers by using the smaller units:
"Some estimate that Satoshi himself may own around 1 million bitcoin" or "...1 trillion zib".
"MtGox misplaced 850 thousand bitcoin" or "... 850 billion zib".