You can't separate "speculation" from any other sort of demand. Demand for monetary liquidity comes from all kinds of sources.

I'm just pointing out that a fixed supply commodity - whether it's electronic or physical - is no use as a trading currency in an advanced economy unless it has a huge derivatives layer pasted on top of it that accommodates stable prices.

Here's more granular example that might be easier to understand and doesn't involve central banks  

Lets say you're a U.S. manufacturing company that makes teddy bears for the European market. You expect to sell $5 Million worth of teddy bears in Europe in the next 6 months and so you budget your manufacturing costs and production schedule accordingly to come in on a 30% margin, 5% of which is net profit.

So you expect an income of $5M denominated in Euros over the next 6 months which means you've got massive exchange rate exposure which could leave you at a loss in 6 months time, even though you did everything right, came in on budget and met your sales targets.

To avoid that situation, you purchase a hedging derivative such as a currency swap or Euro put option to cover 4.4M Euros which is the euro equivalent of your anticipated income at the start of the budget period.

--- Now: Lets asses the situation at the start of trading ---

Without even selling anything, you've just expanded the money supply by a few percent in the derivatives layer (which is basically a higher order extension of a base money supply). That derivatives layer then develops a life of its own - even when you no longer have use for it as follows...

Lets say it's 5 months later and the exchange rate moved against you by 20%. Your put option is now worth 1 million (20% of $5 million) dollars but you only made $4 million in sales. So you will get more on the open market by selling your option than you will by exercising it. A whole new monetary layer therefore opens up that's potentially even bigger than the base layer but which has the same effect of expanding the money supply (or making bitcoin's supply 'unlimited').

Advanced economies have massively complex layered monetary systems. You can't just say bitcoin's going to take over and expect everything to be denominated in units of a deflationary asset. It's ludicrous and ain't gonna happen.

Bitcoin is a monetary asset like gold and is far more mobile than gold, so it will probably have a role in trade to a greater extent than gold did. But it's unlikely to ever actually be adopted as a mainstream trading currency denomination IMO.