Finally got some time to program the most basic keystroke effect:

The code for it is rather simple:

    def update_lights(self):
        i = 0
        y = 0
        dt = time.monotonic() - self.key_time
        for x in range(10):
            self.leds[i] = self.light(x, y, dt)
            i += 1
        y += 1
        for x in range(9, -1, -1):
            self.leds[i] = self.light(x, y, dt)
            i += 1
        y += 1
        for x in range(10):
            self.leds[i] = self.light(x, y, dt)
            i += 1
        y += 1
        for x in range(9, -1, -1):
            self.leds[i] = self.light(x, y, dt)
            i += 1
        self.leds.show()

    def light(self, x, y, dt):
        r2 = (x - self.key_x) ** 2 + (y - self.key_y) ** 2
        c = 255 - min(255, r2 * 30 + (dt * 10) ** 2)
        return c, x * 25, min(255, y * 50)

The key_x, key_y and key_time are getting saved in the matrix scan routine when a key is detected to be pressed.