Many homeowners experienced this exact thing in 2008. The reason this crashed the economy, is that so much new debt had been created that income necessary to pay it didn't exist.
We are in an even worse position now, as the solution undertaken then was to create 5X the number of dollars that then existed, which were given to the banksters - not the debtors, who went bankrupt - and those banksters simply added zeroes to their balances such that they were then solvent.
Once they were solvent, they proceeded to do the EXACT SAME THING and recreate the bubbles.
It will crash in 2018.
Think BTC mooned lately? I am confident that John Macafee's dick is safe, despite his promise to eat it on live TV if BTC didn't reach (some outrageous sum by some too early date). Given the non-inflationary, non-debt basis for BTC, I believe $100k valuation by the end of 2018 is conservative.
As bubbles pop, and BTC moons, those $100T's of phantom dollars will be owned either by extremely stupid people (which, seeing as they own that money, isn't likely) or it will be invested in BTC and other IMMUNE cryptocurrencies by smart investors.
What will $100T influx do to BTC price? How about 5X that? That will be BTC moon.
Today is still before the beginning.
I am not an advisor. I don't know what the hell I am talking about, and am probably insane. If you follow my opinions, which come from an anonymous shitposter on an internet kelp-pickling forum, as investment advice, you are probably insane too. Don't do that!
John Macafee is certifiably insane, also.
Don't be John Macafee!
Edit: oh yeah, those unfortunate homeowners who risk being upside down in their mortgages? If they aren't stupid, when they have enough equity in their homes due to real estate bubble causing valuation to greatly exceed what they owe in their mortgages, they'll take out second mortgages and buy BTC, LTC, or any solid (non-scam) cryptocoin.
Then, they'll be fine.