I really like the look of this, and I can definitely see it being useful. I'm not 100% sure on the pro version idea though - the thing that I love about it is it's simplicity, and "more features" sounds like it might take away from that.

Having said that, there might be a market out there for people who want extra features - but the advice I'd give is to not just add on a Pro package for the sake of making money. Think about what could be of value to developers - whether it's a source of beta-testers, or a list of people who are ready to sign-up to their app when it's live.