Just by way of information for Colin (though I'm not sure how much information it really gives): this comment is currently on +25, which to my mind suggests tha

Just by way of information for Colin (though I'm not sure how much information it really gives): this comment is currently on +25, which to my mind suggests that there are a reasonable number of others who would also like this feature. I think the ability to do a dry-run upload without prepaying (which Colin has already said is on the way) will be pretty much a complete solution.