@Chen, I am a little bit irritated about you regularly questioning basic premises, you reasonably set for this project months ago. Surely doing checks & balances is basically always a good thing, but re-evaluating fundamental cornerstones of this project again and again will lead (this project) nowhere.

From what I gathered in this thread months ago, your plan (and IMO the only feasible route for a project initially producing 3000 to 5000 devices, while hoping for more) is:

1. Take an existing Qualcomm design as a basis.
2. Create a new housing based on your Moto-Z keyboard, with a replaceable battery under the keyboard (to achieve a proper weight distribution, when the hardware keyboard is slid out).
3. Adapt the existing PCB slightly to accommodate for the new keyboard connector and the relocated battery. Do absolutely avoid changing any high-frequency PCB traces, i.e. those connecting the SoC with the RAM, the analog WLAN circuitry, the analog Bluetooth circuitry and the mobile network circuitry. Keep all other changes to the existing PCB as minimal as possible, otherwise you will likely end up in months of hardware debugging, PCB simulations and the costs for a PCB design expert (or even worse with not properly working devices). We have seen that many times in the last 10 years, e.g. Openmoko GTA-01, -02, -03 and -04, Neo900, Pandora, Pyra etc. with only half of them succeeding after years of delays.
4. Deliver the device with LineageOS preinstalled; this requires basing on a design which is already supported by LineageOS, otherwise you will be drafted into significant kernel adaptation work, which can easily stall this project for many months, too. Although some adaptation is likely to be necessary for the hardware keyboard, which is more than enough, IMO.
5. Deliver the device with an unlocked boot-loader or (if regulatory requirements demand that) with an easily unlockable boot-loader (from within Android/LineageOS, e.g. as in Xperia X's latest OS release).
6. Negotiate and settle a SailfishOS option with Jolla, before starting the crowdfunding campaign for the device; again low-level software adaptations are required for this, but having an Android-kernel from LineageOS supporting your device will ensure that all pieces are already there, they "just" need to be integrated into the "Android-kernel" used by Jolla (taking weeks to months). Hence choosing a design as a basis, which is somewhat similar to the Xperia X (i.e. Qualcomm Snapdragon 65x SoC, maybe also some of the peripheral chips, e.g. Bluetooth etc.) will reduce this adaptation work a lot.

The only other option to deviate from the base design, which does not require tremendous efforts, if carried out carefully, is the display: Please do not pick any higher resolution than "FullHD" (i.e. 1920x1080/1200 pixels), rather go for a 1280x720 px display or something slightly higher (e.g. 1440x900, 1600x1080). Very high resolution displays have significant drawbacks, e.g. (in descending order) power consumption, drawing speed (2D and 3D, due to many more pixels need to be drawn), maximal brightness, longevity etc.
Side note: A matte ("non-glaring") display (option) would be nice (I personally prefer them a lot), but requires a non-HighRes display (i.e. 1280x720 on 5,5" to 6", at most 1440x900 on a 6" to 6,5" screen), as the grainyness of the matte surface interferes with the extremely tiny pixels of HighRes displays, leading to an "unsharp" visual impression.