I also like the buttons on my Galaxy S3. But I’m not too concerned about it anymore.
You can also see it this way:
The Librem screen is longer than many others, as it has a 18:9 (2:1) instead of 16:9 form factor.
(Also see Size comparison to other phones)
So, you could argue, the screen has been extended by 40 pixels to provide a much more flexible button area than you would have otherwise. And you can also use it to display content.
No matter if on-screen buttons or gestures, the Librem 5 is well suited for all approaches. And if there’s demand, there’ll be a solution 
I mean, with Gnome mobile, Plasma mobile and UBports we already have three options to chose from and/or change & customize to our liking. Which other phone ever gave you this much freedom? 