I’d rather have a Bridge for Android and the calendar, than a glorified PWA for Desktop.
I have Linux machine. Will probably try it out once they distribute it as a Flatpak on Flathub.
An update from Proton Support:
Mobile-friendly link:
This is why the bridge and other mail clients are more powerful and flexible. It doesnt need the net to work all the time (only when sending and receiving).
@HauntSanctuary what email client are you using with Bridge? I’d love to use it but not sure of which client to use with it. I’m on Linux
Thunderbird is a great client IMO, I don’t use Proton, but if you are just looking for email client recommendations, Thunderbird is very good
proton mail bridge is amazing, especially to have all my emails offline, not to mention I can back them up in my preferred format through plug-ins in thunderbird.
I still do want there to be an desktop app, even if it’s just a wrapper for the web app.
I mainly use Evolution. Its a nice set of features while minimizing eyesore while on a GNOME DE.
And just to confirm, I do use Thunderbird with Proton Mail Bridge and it works well on the email side (Bridge not supporting calendar is a whole other issue).
I had a bizarre experience with this app. I installed the beta, and it told me I need a paid account. I thought “OK, I’ll wait for it to leave beta”
It has now left beta, and I decided to start it again and after updating it tells me my “free trial” is over.
And here I was hoping this would be available for all to use.
I really dont undestand why they prioritized an electron desktop client over implementing calendar and contacts along with their bridging software. Its a facade for the normies 
Certainly is, because as a “normie”/layperson I have no idea what you are talking about.