However, I read somewhere that most users of Zcash do not even turn on the privacy feature as it is optional so most of the transactions are public. And I assume similar will be applicable to Dash as its privacy feature is also optional. So it seems that current demand for anonymity is not that high as some people expect.
The optional thing was mentioned in the article. Because of this, most people just use Zcash without going for privacy. That's why I really like Monero where privacy is must- no optional.
It doesn't make sense to send up to 10 million onions
If you don't offer the feature they need, how will they use it? Imagine, one user want to use DeepSend to have untraceable payment. He want to send 10000 ONION worth of $600, will he have the patient of sending 10 times or he will just ignore ONION and use XMR? What do you think?