It does not need to be changed at the protocol level. But adoption rate would probably improve if two things happened.
First, there needs to be better, smaller, catchier names for the smaller units than "millibitcoins" and "microbitcoins". Names that don't sound inherently fractional. Especially the millibitcoin, as it currently approximates to dollar parity.
Second, apps need to use these smaller names with these smaller denominations by default.
Unfortunately, this is one of the downsides of decentralization. After the conventions were decided at the beginning, they've since been impossible to improve upon.