Stats update:
2017-10-26: crossed 3000 ordered devices
2018-10-15: crossed 4000 ordered devices (almost exactly 4 months after crossing 3500)
September: +180 phones (+6,9%) !!!
October: + 109 phones (+4,2%)
So, 4068 preordered devices as of today, including bundles.
And consistently more than 100 preorders/month for the last 4 months. (106…180, 130 on average)
That might already be sufficient for being sustainable, but hopefully that number will grow even more when the phone is actually on stock.
250/month would be a good start 
This would still only mean 3000 to be manufactured per year, which is not much if one expects prices to go down and development (rev2) to continue.
Funding currently grows about $100,000 per month, so we’d reach $3 million by the end of the year, doubling the campaign goal. I’d love to hit at least the first stretch goal (4 million), just because, but I guess we won’t…