What is this about customers and business? Bitcoin is not a business. After all this time you've been thinking of Bitcoin as a product that you're selling people on? p2p cash is not just cash for cash's sake. It is money and money is a social construct. Bitcoin is also a social construct, not a business or a product that is being sold to customers.

I don't know if you know this, but you can very much run drivechains right now. Its considered a brittle fork (that's my name for it) whereas a merge would be a softfork. The difference is that if your brittle fork client loses consensus at any point, it is no longer considered Bitcoin, but if a brittle fork client becomes a soft fork through shear adoption, it becomes Bitcoin

So if this is really such an in-demand feature that people would like to make into the social construct we call Bitcoin, then LET THEM RUN FULL NODES

That being said, it sounds like you don't understand why Bitcoin doesn't use zerocash. We want blockchain auditability. We had a buffer overflow once upon a time and seeing that transaction create Bitcoin out of thin air was important to the participants who all decided to pick up mining an older state of the chain which was not above the 21 million limit, with a new client that had the patch as well as a hard coded cap rather than the implied cap of the miner subsidy.

Now, smart wallets is a thing I've never heard of before. That is its own topic though.