If most people use smartphones to consume content on metered internet connections with limited battery life, where do they pin it such that it's available to others?
In one futurist vision, your home router/gateway modem could provide this service (and also be powerful enough to host game servers if you start up their clients on your phone while on that modem’s LAN.)
A lot of people still have a "real" computer they do a lot of browsing on - it's just increasingly that "real computer" is a laptop, rather than a desktop, computer.
Let's assume these figures are useful as a first approximation of the number of hours of laptop usage per laptop owner in 2018. I'm not saying it's a perfect match, just that they're likely to be better than figures you or I would pull out of the air.
Taking the centre of each band, assuming "more than 10 hours" means "10 to 16 hours", and excluding the "no computers" band, gives a mean of 4.3 hours per day. So each laptop is active roughly 18% of the time.
That's more than I expected, but it still means you're going to need a lot of people to pin the content before you have a 99% chance of at least one copy being online at any given time.
Edit: As far as I can tell, with 18% uptime you need 15 copies for 99% reliability (assuming no correlation between the online times of the various copies, which is optimistic - in reality there will be strong daily and weekly cycles).
Maybe just publish what you've downloaded while charging. Much like most intensive things like say picture backups that often are done only on wifi and only when charging.