This makes no difference.. it's not about allowing the user to change denomination in the client... it's about what is the default denomination and even more important, what is the default in spoken language, like it doesn't matter what is the default in the wallet if on TV they speak 1BTC = 600USD
There is no default. Bitcoin is not a centrally managed stock where a split can occur overnight and everyone has to switch. Coinbase could make their client bits by default but that doesn't mean other people or services have to do the same. Industry standard will likely slowly transition to bits but is not required. It is a choice.
Technically yes, there is no default.
But in real life, there is a kind of consensus that BTC is equal to 100,000,000 satoshis right? Isn't this the default? It's the default in most software and also in spoken language.
Exactly, but Coinbase's 100 satoshis = 1 bit is not yet really a general concensus default, but it makes sense and it will make even more sense if prices rise.