Crypto-tokens/iota is a different beast but human psychology is still the same. We will probably be in a better place post-launch considering the anticipation of iotas, but even if we get a 5% commitment before launch, I'd be shocked to see 75% of those funders pay up.
You are very optimistic about human nature. In US, the average church goers' donation to church is about 3% of their income while they are supposed to donation 10%. So my estimate is 30% of pledged iota to be actually collected after the official launch. Don't count anything after iota hits the exchanges. That is just the reality. I am not saying there won't be a few people who will 100% honor their promises. but they just can't cover the overall loss.
I doubt that voting will work because most of people won't participate and there is no a good and easy voting mechanism now and we don't have time to wait for them to show up in months.
The best and fairest and easiest way to do this is to create extra 8% to 10% of iotacoins from the genesis before the official launch for the foundation and the deals. No one needs to donate anything any more and we save the uncertainty and hassle to collect the donation. And the cost of creating the extra 8%-10% of iotacoins will be equally and proportionally shared by everyone and everyone can proudly announce that he/she is a part of it and it can guarantee the foundation have enough funds to start with.