These people use museum endowment as an analogy, but especially judging from that analogy I don't think they have any idea how this thing works. Storing someone else's data forever is completely different from how museum is run. The analogy is so ridiculous that it's not even funny.
Where this analogy may apply is sites like Waybackmachine, because they're at least doing it for the greater good. But I'm pretty sure these guys will throw away some random guy's private file archive the moment they run out of money.
Normally I'm all for silly experiments that come from ignorance, and I'm fine with various consumer startups that come and go along with their user data, because sometimes this ignorance leads to success. But in this case these people are playing with someone else's data AND asking for money, and claiming to store these forever in my view is no different from a scam artist. Intentional or not, this to me is no different from a scam.
I would say the companies who are at least honest about exploiting our data such as Google and Facebook are more ethical.