That's a tricky one.
While that sucks for people who can't continuously support I can understand why Dev is doing this.
I myself can't afford it but ALWAYS buy ~10 bucks subscriptions for the 5 games I really enjoy when a new update drops regardless of leaks or not. I started playing this game with 0.3 and was ready to get a sub for the new release (and probably will if it leaks still lol).
That being said, the other games I'm not lurking around everyday I don't tend to support. I highly doubt there's enough people who are on a similar middle ground to make the risk worthwile for the developer. As soon as it leaks, 99% of potential new patrons won't subscribe.
There's basically no incentive anymore to sub to get the game earlier (because you don't get it

). Yes he might be shutting the door to potential subs but I also see it as an effective way to rightfully prevent leaks. I don't think someone ready to commit for effectively 2 months (initial sub + the 30 day period which would coincide with a renewal) would be willing to leak it.
I think overall it's out for the best.