Only time will tell, but I think that the subscriptions will hurt Scirra in the long run:
Let's say that the average lifetime of C3 will be around 5 years (like C2 is now):
C2: 5 users -> 5 x 100$
C3: 1 user -> 1 x 500$
So for the same money, you could have 5 users that would use the product, develop plugins and make publicity for Construct instead of only one user.
Yes, you can argue that C3: 5 users -> 5 x 500$ (five times more than C2: 5 users), but is clear that C3 userbase will not surpass current C2 userbase.
In my opinion Construct downgraded from competing with Fusion and Game Maker, to competing with Stencyl and Game Salad.
By no means C3 is a bad software, on contrary, is actually a miracle of new technologies and shows the power of HTML5/Javascript, but it falls short in the current gaming industry