Assuming all of the ~200,000 kickstarter backers would have been okay with the $10/year software, and no duplication of backers between their three campaigns, and that yearly payment kicking in as soon as each of the three campaigns ended (so before the customers even got their devices), that would have brought in a bit shy of $5m, compared to the ~$43m they brought in from their three campaigns. It's a good thought, but I doubt their revenue stream was only 10% away from being sustainable.
I was assuming a flat "free" boost to their total revenue stream, so my assumption was even more generous than yours.
I sincerely doubt they were only 10% of revenue away from being solvent, even if it was money that came out of nowhere. Reports I've heard are that Fitbit paid ~40m to pay off Pebble's debts, meaning that instead of $10/yr the subscription fee would have to have been closer to $10/mo.
