LOL it's going to be far more than just 700,000 now you really are guessing, there's no way of telling for sure though because there is no data on the cryptocurrency users, that's how the system was designed so people couldn't be nosy buggers and spy on somebody's wealth.

In terms of value. Marketcap of BTC is 10B$. Total global assets is on the order of 1000T$. So roughly 0.001% of global assets is Bitcoin. Its still less than say the #100 biggest US corporation.

In terms of users. Coinbase is perhaps a good measure. If they have 700k users, it should be say 100x that globally, but that seems a little high. 5-10 million seems right, but question is how much they use it. it would be very interesting to some data in terms of distribution of countries.