It seems like you are misunderstanding something. There are two different issues: integers vs decimal points and size of measuring unit. To illustrate, suppose there were 21 billion and not 21 million bitcoin "units" in Bitcoin. Still all integers, decimal points don't come into it. If we today converted each 1 satoshi into 1000 of "new satoshis", nothing has changed, except a measuring unit. It does not represent "inflation" as some brain dead "economics experts" on twatter think. (just to clarify, such a 1 to 1000 change would be extremely non-trivial code-wise and ecosystem-wise (but not protocol-wise!) .. if nothing else, making it backward compatible sounds not very fun).