What if I said I wanted to borrow $100 from you and pay you back $99 five years later? Would you do it?
Actually the answer is
Yes. If you are doing full reserve. This is precisely how a full reserve bank earns its money, in exchange of keeping yours safe and giving it to no one.
If the bank doing it is a fractional reserve bank (as most likely is) then it makes no sense, and might in fact cause a bank run.
How does this help Bitcoin? Its a bit unrelated. When you send bitcoin to an exchange or online wallet, you are losing money on transfer fees and often the site's fee. Which is not unlike "negative" interest (which is another way of taking fees).
But in an actual deflationary economy this should be the norm, not the exception. People should by default be asked fees to deposit their money in a bank that will absolutely never use it for anything else. This type of bank can never have a bank run, everyone could withdraw all their money at anytime, unlike fractional reserve bank.
Perhaps this is an effect of certain deflationary coin spreading worldwide... But start learning how a deflationary economy works, you need to read
Mises and the Austrian economists, read about full reserve banking among other things. What you think crazy is actually right, once you learn the missing parts.
In a deflationary economy people tend to save money (ie. hold) and use only what is needed. But this money/investment is solid and unchained to debts or absurd terms. It is like your savings grow in purchasing power, so its equivalent to the misleading "interest rates". Except, no middlemen are required, they become optional. You pay for someone to keep your money safe because you can't figure it out how to do it yourself.
Sounds familiar? It is. Americans have it hard to understand because they have been used so much to debt and debt based economy, while Austrians propose a savings based economy with a deflationary coin (they wanted to use gold directly, as this was proposed early 20th century, in fact, before that big crash of 29). Oh and bubbles never form in this type of economy, so there are no crashes either. Everything moves steady, and slowly, instead of fast and furious only to crash hard.
Read the Austrian economists and you'll get it.