Hey guys,
tons of thanks for the feedback - this helps me a lot!
So the advantage to me is that I do not have to worry if my computer fails, gets stolen (assuming I encrypted my wallet).
How often could I backup? I think the ease of doing the backup is going to define your market.
I would still have the fear of someone hacking my machine and just transferring the coins away though. I could, however, take the orriginal option and store the coins in a separate wallet if I wanted.
How many wallets can I store?
Exactly. It's not something like a cloud wallet, it's a wallet backup service. You can backup as many wallets as you want. Also, to ensure your Bitcoins are safe if your machine gets hacked, the safest thing to do is to have a strong wallet password, because then the hacker can't do anything with your wallet file.
I would be more concern with an attack from within. You can make it very hard to get into a place, however, if there are employees inside then there are already people inside that can do some damage of theft.
I think I forgot to say that: My idea was to put a safe in one of the bunker server rooms. I will be the only person who knows the number. The number will also be stored in a safe at my local bank. In case of death, an involved, trustworthy person, i.e. parents, brother, wife,.. will be allowed to open the bank safe and make further steps. Another idea was to rent a complete room in the bunker, but it's much more expensive and highly depends on how many people would use my service.
I think there is a need for the service, the question is how much and who?
This is the golden question

I also posted my idea on Bitcoin/Litecoin Reddit subforums to get more feedback, but it was not recognized in the flood of new threads that arrive there every minute.
You might want to try
https://cryptostocks.com/ for funding. It would help with the marketing as well since the people who might use the service are some of the people that provide the money.
Thank you for the link!
