You're right. Show HN is for things that can be tried out now. It's ok if people have to download an app to do that. But an email signup to get "early invites by May" does not count—it's the very thing that rule was written to exclude.
If your work isn't ready for people to try out yet, please don't put "Show HN" in the title. Once it's ready, come back and share it then.https://news.ycombinator.com/showhn.html
It's good for the community to tell us about these, since we can't notice them all. In the future, you (or anyone) are welcome to email us at hn@ycombinator.com to make sure we look at it.
If your work isn't ready for people to try out yet, please don't put "Show HN" in the title. Once it's ready, come back and share it then. https://news.ycombinator.com/showhn.html
It's good for the community to tell us about these, since we can't notice them all. In the future, you (or anyone) are welcome to email us at hn@ycombinator.com to make sure we look at it.