Is 2100 trillion really enough? If the GDP of the US was 15 Trillion dollars last year, and each of those dollars is divisible by 100 cents, that's a lot of 'units' (more zero's then I care to write).
Wikipedia says the total money supply in circulation of the world was 4 trillion in 2008 which had doubled from 2 trillion only 6 years prior (and had doubled from only 1 trillion 12 years before that). They don't mention the current estimated money in circulation, one could perhaps guess that it's up to 8 trillion depending on how the recession has panned out.
Maybe our incredibly large number won't stay so incredibly large for as long as we might think.
You cannot inflate btc like you can with money those dollars are fake made up from thin air ie. they just turned the printing presses on nothing backs them. Now you can say nothing backs btc either but one thing you can be certain of is no more than 21M of them will be produced no printing press to turn on here to get more.
I think it will be enough for the next few decades. By then there will be all sorts of new crypto currencies, so who knows if Bitcoin will still be the primary digital currency for daily exchanges.
Also, I'd keep in mind that by then, a large portion of BTC will have been lost, so 2100 trillion will never really be in circulation.
Assuming no one ever breaks the encryption. It was said that everyone alive today will be dead by the time that happens