A subscribe feature requires tracking users with their user logins. We do not track users and spy on their data. Therefore, a subscribe feature will not be available.
Instead, we've also rolled out the RSS feeds feature, which now shows an "RSS FEED" red button at the top of your channel page.
This RSS feed allows anyone running RSS software to "subscribe" to your video feed, meaning they will receive automatic alerts when you publish new videos.
The software that end users need to use is called "RSS reader" software, and there are many open source RSS readers readily available.