In comparison to most GUI apps on Linux, this looks pretty good. It might not be perfect, but if i had to choose between no linux port, and a good-enough linux port, i'll choose the latter.
It looks "good", but not, as claimed by the Nylas team, "native".
Even Swing and JavaFX manage to make better looking, faster running, easier to code UI apps, which can be distributed smaller (the Java Runtime, thanks to Jigsaw, is smaller than the node+Chrome runtime of electron)
The problem with asking for a GNU/Linux standard application is there are several toolkits for developing them that stand out when not in the same base as the desktop environment. There is a single concise appearance to certain distros (e.g. Elementary), then difference of appearance in desktop environments (e.g. GNOME, KDE) and then there are the toolkits that are written completely different and use separate libraries (e.g. Qt, GTK).
By asking for a "Linux native application", you would need to create forks for GTK/Qt theming at the minimum and change the appearance altogether. It's just an absurd request really. One thing Electron does not do well is per-system graphical elements. It renders the same on every system so you either have a unique application design or you're conforming more to Window, Mac, or GNU/Linux. Or doom yourself to an old stale design, which is bland enough to fit in every category, but isn't the aim of the project.
You realize that GTK and Qt are both compatible with the other?
Most GTK apps work nicely under Qt (although this is very suboptimal), but especially Qt apps look native everywhere. From windows to mac to KDE-environments to Gtk-environments.
What do you mean by gtk under Qt? What about Tk apps, or Athena apps, or Motif, or GNUStep, etc.? There really is no such thing as a native Linux look and feel, you just happen to use a consistent selection of apps on your own system.
What I mean is that a Qt app will look native everywhere, and Gtk apps will look native in most places.
Most other toolkits, as you mentioned, don’t look native in many places, but Qt natively supports the CDE style, the Motif style, all different Windows and Mac styles, etc.
A Qt app looks native on Mac OSX, on Solaris, under Gnome, under KDE, under Windows XP, under Windows 10.
That’s why I avoid apps that aren’t either native or Qt anywhere, no matter if I am running Gnome or Windows, KDE or Mac.
There basically is. Linux per se is just not a desktop OS, like Windows or OS X. Ubuntu has a standard UI, Debian's default install has a standard UI, Kubuntu has a standard UI, and so on.
That's even worse though. You can't ask for a universal GNU/Linux native appearance since there are Debian/Kubuntu/Ubuntu standards for UI. The list goes on and on too.
Even Swing and JavaFX manage to make better looking, faster running, easier to code UI apps, which can be distributed smaller (the Java Runtime, thanks to Jigsaw, is smaller than the node+Chrome runtime of electron)