I don't understand how you could use newsgroups for storage, except in a "I don't care about data loss" kind of way. I haven't used USENET in decades, but NNTP is a messaging protocol it says nothing about storage AFAIK. I do recall that back in the day, messages in busy newsgroups would expire rather quickly (probably due to limited storage on my news server at the time). So if I post a message containing my backup to a binary newsgroup, what assurance do I have that I will be able to get it back?
Commercial binary NNTP providers have basically infinite retention at this point, if your content doesn't generate DMCA takedown requests. E.g. http://www.news.astraweb.com/ $10/mo gets you 2660 days (>7 years) of retention, growing at roughly one day per day. (Four years ago, 3 years of retention was common.) There are also pay-by-download-in-GB a la carte plans that would be good for backup-only use (because upload is free).
Even if it isn't infinite, you can download and repost every 7 years if you care about having backups for longer than that.
