Hi Chen !
I never tried borderless screen, but can give you another feedback, if it can broaden the question.

I installed this weekend the community port of Sailfish on my PhotonQ (with hardware keyboard). It works great, but I had the opposite problem: the casing around the screen goes a slight bit above it, making edge swipes a pain as the casing prevents the finger to touch right on the edge of the screen.

Doing so, I compared it with the Jolla 1 (and my previous N8), and found 2 things to take into account in regards of edges: comfort to hold, and edge swipes:
* N8 was great to hold, as it is thick enough, and the edge shape is mostly round. (The same shape was later used on N9 with curved screen to use edge swipes, and your concept looks a lot like it)
* Jolla 1 is not so great to hold due to the edge being in 2 parts (the TOH concept with one half flat, and the other half rounded), but on edge around the screen is a bit rounded to allow easily reaching the edges with the thumb. I never had trouble activating it.
* PhotonQ is in the middle regarding the comfort to hold, as it shape is continuous, but still more angular than the N8, and a said above, the casing makes it a difficult to kick edge swipes (top and bottom swipes are ok).

About borders, older phone had really huge border that should be possible to reduce without introducing problems regarding edge swipes, but I would not go above the point where the digitizer reach a zone where you hand is naturally resting while you hold the phone (firmly, like while walking). That may be only 1 or 2 mm from the outer dimension probably, not more, but depending on the shape of the phone (edges roundness, thickness, width), the resting position may change a bit. I will try tommorow to borrow a friend's S8 to make a few tests and see how the edge is actually accessible to confirm this though.
If it is easier to get border-less screens (as it is the new trend), then there may be some software mitigation possible to handle it (increase the range for edge swipe, disable a few pixels on the sides, palm filter like on touchpads)... ?

Finally, with a hardware keyboard, screen real estate is a little bit less important than without, as you don't cut the screen in half to put a virtual keyboard in it for most things. Some will still want bigger screens for tasks done without the hardware keyboard, like using it vertically, watching video or reading website.