it will suffer from MASSIVE deflation as its value spikes to $10+k to 1 BTC
The deflation of BTC as it appreciates does seem to be a significant problem. It will really encourage people to hang on to the currency instead of spend it. Why would I buy a pound of coffee this week for 3BTC if I could buy one next week for 2BTC. I've not seen anyone address this.
If entire world only used BTC, the value would have to be millions of dollars per 1 BTC. ha!!
Yes, but that is actually built into the idea of the system. For that reason bitcoins are divisible up to 8 decimal places. As the value goes up, you end up working with smaller divisions of the currency's base unit, just as with inflation you end up using higer multiples of the base currency. It cost 200USD in todays currency to buy what you might for 10USD in 1900. Effectively if the entire planet was using BTC we'd all be paying for things in nano BTC, no problem.