Correct, so we could arbitrarily agree as a community that the old mBTC is the "New BTC" and that there are 21 Billion "New BTC" available.
What if everyone doesn't agree? I don't. So yes as I pointed out if you have complete unanimous agreement of every coinholders, merchant, developer, exchange, etc then sure you can make a change. Baring that what happens when some sites start advertising prices in old BTC and some in new BTC? Someone on new version of client sends 1 BTC to someone with newever version of client. Each one things the other messed up because on their clients they see a different amount. MtGox prices in "old BTC" but doesn't call it old BTC it simply is BTC and BTC-e prices in "new BTC" but also calls it BTC.
Quick 1.23 BTC is it old BTC or new BTC?
It isn't going to happen just like tomorrow we could decide a meter isn't a meter it is a "new meter" which will also confusingly be called a meter expect it is 3x as long as an "old meter" which will also be called a meter. That could happen, but it won't because it would be stupid and pointless.
Of course, the real issue is that it becomes uneconomical to send less than 1 mBTC (100,000 Satoshis) and have it confirmed quickly due to fees that the client and/or miners require. Fees will only get more expensive as traffic increases. There are other threads looking at that issue though.
Fees have been reduced in the past, will be reduced again in the next version, and will likely be continually reduced and decentralized more in the future.
There is no required fee on high priority transactions. The min mandatory fee only exists as a spam prevention mechanism to protect the network from Denial Of Service attacks. It can be continually lowered to a point which balances the needs of the network with the need to protect the network.
I'm not advocating any deliberate change in the language of units of measure of Bitcoins, I'm just predicting that it'll happen organically. Because language often takes it's own direction, and it doesn't matter if there is unanimous agreement or not. When someone says they want 20 bitcoins for a pair of alpaca socks, the context will be enough for most people to realize they mean 20 mBTC.
It's obvious that later adapters will prefer to count coins at the level of mBTC because the human mind prefers whole numbers over decimals (567 mBTC is slightly more preferable than 0.567 BTC). The interesting question is, "What will the average person call that unit of measurement?" If Bitcoin truly starts to gain wide acceptance, I'd bet they won't pronounce it "m-B-T-C" That's 4 syllables, are you kidding me? Name a world currency that is more than 2 syllables long, because there's not any. But will people pronounce it as "m-bits", "bits", "mibs", "mits", or risk confusion as just say "bitcoins"?
Personally, I like "bits" because it's short, implies bitcoin, and the context should make it clear that it's not another currency. Just my two "bits"
