Earlier quoted context omitted.
It's frustrating that we can't use the product yet, but I'm sure that people's reaction here will go a long way in helping them gauge interest.
Though this is reasonable, I wonder if it's measuring the right thing. Since money isn't involved (as far as I know), people could be entering their email just out of curiosity. It's easy to provide an email for a notification of completion, after which, make a decision to continue with participation or move on entirely.
It isn't something where you say yes/no based on the number of signups.