I already pay GitHub monthly because I have some repos that I want private. I'm a solo dev, only hacking on side projects that may or may not be something one day, but want to keep them private anyway. My bill is about to go down, and my benefits go up. All in all, I'm quite alright with this change, agree that it's positive.
I get that it gets worse if I ever take on N number of developers, but that's a hurdle I'll deal with if I ever get there. I do imagine I'm not alone in this position.
The number of times I've wanted to search a repo for something only to have to clone it and search in my IDE is staggering.
Rather than completely limiting private repos in their old pricing model, they could have limited "active" repos, and created an archive feature, where archived repos were not available via Git, but still existed as backups and in case you ever wanted to make them active again.
I do, however, believe that the new, per-user pricing is more sustainable. File storage is rather cheap; running Git pull / push is not necessarily.
I don't have any numbers on how people structure their accounts on Github, but my feeling is that this is a positive change for the majority of Github users.
Git encourages having many smaller repos for modules over massive single repos. $1/repo/month is fine for active projects, but gets expensive really fast if you want to keep archives of small private experiments around. Because of the per-repo pricing on Github, I've seen many friends and startups I've worked with keeping their open-source public repos on Github (for free), while moving private repos to Bitbucket.
I would not be surprised if this pricing change would be a net revenue loss for Github, but still implemented to avoid losing market share to Bitbucket.