That's me in a Bit coin farm. I include it here as a curiosity and to let you know that I have actually spent time looking into it. (I also have a master in computer Science, if that helps).
I think that Crypto currencies are here to stay but I don't see them as a good investment, and they are not, currently, a real currency either, because their value changes too much, too frequently. They can be used as a hedge for your investments and any allocation shouldn't be more than 2% to 5% of your net worth.
Having said that, I don't intend to engage in crypto currency discussions in general but only in what regards the original posting: Using crypto as collateral for buying real estate.
I visited the website of this company that offers the loan and their offer is pretty straightforward: You put bitcoin for a value of X dollars and they lend you that very same amount at around 4% rate.
The way it works, I presume, its like borrowing money on margin from your broker. In the margin loan, you can get a % of the value of your deposits and you can use it to buy more stocks or to do whatever. The BIG issue is that you must maintain collateral, if the stock value takes a dive, you must pony out the missing collateral in a matter of days or your stock will be sold, at whatever low price it might be, to satisfy the minimum collateral required.
In the case of this Crypto loan, I assume its a similar situation, you must put more crypto as collateral if it drops in price. Since crypto prices vary wildly, you must have a good reserve of crypto or cash to provide the collateral. Imagine you buy a $500,000 house and put $500,000 worth of bitcoin as deposit but the bitcoin value drops to 50%, (as has happened before,) now you have to come up with $250,000 right away. Would that work for you?
A loan of this kind would be good for a an investor only if they truly believe that the crypto will increase in value for more than 4% a year for a number of years to come and you must have 2 to 3 times the value of the property in bitcoin to buy a property. I think that takes a lot of faith in crypto but this lender will have some takers for their offer.