Self managed encryption keys is not "hard" any more than any other secure web service. I can't imagine why you think that this would have any effect on features other than from a cost benefit perspective.
Linux support is fine, if you're willing to accept HTML5 and JavaScript executing who knows what in your browser.
If evernote can't make a good text editor with HTML5 and JavaScript then it proves that apps in the browser is a dead end. Text editor is basically, the "cost of entry" and if an entire team focused on that single feature can't deliver it after years, well... I'm not really surprised given the state of JavaScript (collectively ruined by Mozilla's lack of resources and Google's ill will) and HTML5 (collectively ruined by nobody giving a shit about the language before their own interests).
Given the crumbling of infrastructure of the web, I'm kind of surprised anyone still uses the internet at all for anything more important than facebook and tabloid news. Maybe nobody does?
like bot detection on NT-based systems? Yes, lets not talk about that.