Currently Bitcoin have +10 millions users, according to Blockchain wallet info. This is very small part of whole world market, so in fact Bitcoin have very small niche, but Bitcoin can expand in future, if large web sites, like Amazon will start to use it.
And 90% of those wallets can be owned by just a couple of people who are running big websites. People can create unlimited number of wallets so those numbers mean nothing at all. It can serve as the upper limit but the actual numbers are really far from that. We're just about a million, more or less. But we keep on increasing in popularity as day goes by since some people are making good money from the bitcoin world and can't keep talking about it to their friends.
You can already purchase things from Amazon with bitcoins using purse.io. It's a third party so it's not really Amazon that accepts bitcoin.
You cannot judge the success of bitcoin by the number of wallets existing as anybody can create tens of thousands of wallets. Also we cannot blindly look at the price of bitcoin climbing up and say more people are coming into bitcoin. It may be some bots or traders pumping up bitcoin.
But I am positive on the growth and adoption of bitcoin. I am dreaming of the day, where even a small kid will know how to use bitcoin! that is my dream for bitcoin. Obviously, there is a long way to go. Right from scaling problems to spreading the bitcoin gospel to all corners of the world.