Market share shouldn't matter.

The numbers that do matter: Are the number of contributors increasing, decreasing, or stable? Are the number of users increasing, decreasing, or stable? Is the rate of increase (if increasing) for either of these itself increasing, decreasing, or stable?

As long as contributors and users are both increasing, you're probably ok. As long as the rates of increase are at least stable, you're ok.

It's not like this is a life or death struggle, emacs will probably outlive us all.

>Growing in terms of the number of users, dwindling in terms of the share among editors

That's as may be. Just because something has a high market share doesn't mean it's the best product.

Chrome is by far the most "popular" browser by market share, and that doesn't stop it from doing all kinds of stuff that benefits Google over users -- often to the detriment of those users.