Board Thread:Support Requests - Designing Your Wiki/@comment-40033769-20190828160850/@comment-5811199-20190901021317

It's possible, but requires knowledge of JavaScript to check number of subscribers.

Note that YouTube is changing the way they show the number of subscribers starting from next week - see https://support.google.com/youtube/thread/6543166 - which will mean that it is probably easier to just type out the number and manually update it.