Won't lie about being a little conflicted. On the one hand, I came upon Construct looking for a free game maker just to tinker around with and then I got way more than I expected in it. On the other hand, as a musician, I completely understand the mentality of wanting to do something that you're good at, that you love and get paid for it, and the generally common consensus that your hard work should be free just because it falls under the realm of entertainment and not necessity. So all in all, I do want to add that I do support your decision to go commercial.
As far as your proposed licensing model goes, I personally think it looks good but I think you should make more distinction between the fact that people are paying for a license rather than continued use of the editor, so that they don't panic like I saw in the other thread before it got locked with worries about their editor locking up on them.
I saw one person on here propose limited features in the free trial a la many other pieces of software. I think what you might be able to do is lock exporting functionality, so that you need to use Construct to run the games on the trial or expired versions, but leave all the actual game creation ability open. That way it'll be more of an inconvenience than a nag screen but not so much that they can't continue work on their game and continue to test it. They just can't make it convenient for others to play, as other folks will have to download Construct in order to play trial games. I think it'd end up win/win.
As for piracy, I've heard it said pirates will be a problem no matter what you do. Which is true. However, the numbers aren't as bad as most people seem to think (I've done some studying). People are willing to pay depending on not only price points they find fair but also if they believe in and appreciate the faces behind the work.
You seem to already have the fair price point, which you can make even more readily apparent by just adding something along the lines that "this translates to only $x.xx a month" or "help support the development of Construct! buy a license!" or some such thing that would be written far better than my 5 second attempt right there.
The other thing you need to worry about is keeping an active and appreciated position in the community, whether it be frequent news/blog posts, getting people's opinions on proposed additions or changes, things like you're already doing. Only thing I can think to suggest you do in addition is to make sure it's readily apparent to new users/members from the get-go who you are (I had no clue as to how important Ashley was to Construct development until probably the beginning of this year, and I started playing with Construct probably second quarter last year ).
I know folks may disagree with the exporter functionality thing on expired licenses, but from what folks have been mostly complaining about (at least before) was that they wouldn't be able to keep working on their games with expired licenses, but if you can devise a way to test games without exporting I think it could be a simple but somewhat significant way to either A) get folks to pay, or B) get more users downloading Construct = more potential licenses or at least word of mouth.