1) HTML/CSS/JS is sill the only truly cross-platform (mac/windows/linux/web/ios/android/etc.) UI platform/ecosystem in 2016, and it will probably stay that way in the foreseeable future because OS makers love their walled gardens.
2) An app's memory efficiency is not a top 10 priority of an average solo-or-small-team developer's concerns, because that's not what most users pay for.
Electron/NW.js apps will only become more common, so I hope things will improve with asm.js/webassembly/etc.