First, lets look at some facts regarding Linux/Unix (go to wikipedia to look at the sources):
"It is a leading operating system on servers and other big iron systems such as mainframe computers and supercomputers:[16][17][18][19] more than 90% of today's 500 fastest supercomputers run some variant of Linux,[20] including the 10 fastest.[21] Linux also runs on embedded systems (devices where the operating system is typically built into the firmware and highly tailored to the system) such as mobile phones, tablet computers, network routers, building automation controls, televisions[22][23] and video game consoles; the Android system in wide use on mobile devices is built on the Linux kernel."
"The Linux market is growing rapidly, and the revenue of servers, desktops, and packaged software running Linux was expected to exceed $35.7 billion by 2008.[91]
"In September 2008 Microsoft CEO Steve Ballmer admitted that 60% of web-servers run Linux versus 40% that run Windows Server.[93]
Primarily based on web server statistics, the estimated market share of Linux on desktop is 1.17%.[94] In comparison, Microsoft operating systems hold more than 85%.[34][35][36][37][38][39][40][95][96]"
Bitcoin, in my mind, is going to be just like Linux. Extremely useful. Technically superior. Shunned by the masses. I don't ever see the average person running around with 30-character, randomized passwords, paper wallets, hardware wallets, checking the blockchain for confirmations. If more than 2% of people aren't willing to install Linux, locate Linux drivers for their devices, and find suitable software for their personal computers to have what most tech geeks would call a superior operating system, then are they going to bother doing all of those geeky things with BTC to become their own bankers? "Online wallets!" you say. Let me convince my parents to put a significant amount of money in an online wallet that's 1 years old.
Most people (85%+ or so) would feel much more comfortable keeping most of their money in fiat in the bank and then paying a third party a small fee to do transactions in BTC on their behalf to reap whatever benefits BTC can afford them. So if a Kenyan living in China wants to send a 10,000 RMB remittance back to Kenya, he can go to Eastern Union Bitcoin, Inc. and hand over the 10,000 RMB. Eastern Union Bitcoin, Inc. will do all the BTC buying/selling and currency conversion from RMB to USD and then hand the money over to the Kenyan's Bitcoin-illiterate, bank account-less family members for a fee much less than Western Union's.
In this way, Bitcoin gets used, but people who aren't ready to handle their own security can still use the fiat system they are used to. Same thing with this Bitcoin ETF. People can invest in bitcoin without having to really get into the nitty gritty. I think bitcoin, if it becomes successful, is going to be like the linux/unix of currency. It'll be operating in the background where and when it makes sense to use it, but the vast majority of users will not be directly working with it for ordinary transactions. They'll interface with BTC through layers of software and 3rd parties in the same way that we all send information through linux-based operating systems on workstations/servers/routers/phones every day but only a small percentage (1%) of us actually mess around with Linux on our desktops.
My prediction is that Bitcoin, at peak adoption, would be used directly by 1% or so of people, but play a much more significant role on the backend of everything. Thus, trying to get merchants to accept BTC directly or trying to get your average Joe on the street to download a wallet and start trading Bitcoins online is not really important. In fact, if someone loses their money due to lack pf technical precautions, it will likely turn them off to BTC forever. The vast majority of people in America and Europe don't need to have a BTC wallet. They'd probably rather buy BTC gift cards at WALMART or go through middlemen while having their money insured, reversible, and sitting in a 100 year old, trusted institution.