Here's my feedback. As a part of a small startup team, I used Jira for years before Github issues and Slack were there.
The company I work at right now still uses Atlassian's trio Jira + Hipchat + Bitbucket. They are great tools with lots of features but Jira's productivity is much slower compared to Github issues and Hipchat offers a poor user experience compared to Slack.
Productivity apps are never in top 10 on app store. The efforts you spent building your app did not pay, but I don't think you should blame app store for that.
I would suggest not to take it as a failure of the mobile app concept. Learn form your experience and think about what you can improve.
Everyone using a browser that doesn't get security patches is basically a walking malware farm. Not supporting them with your site and pushing them to upgrade is the moral high ground.
It's a good first step though. This means that websites can start telling users "we don't support this browser because Microsoft doesn't", etc., and they will die off quicker.
I agree that closing all borders physically would be tough. There would be controls on the roads and airports, but in the zone you posted a physical wall is required to isolate two countries.