@dr_frost_dk
Thanks a lot!

@King Ralphred
No worries, tripod mounting point (screw hole) as a must for big backcover variant (this one that holds bigger battery). As for the camera hole being threaded, I think I - finally, got the idea. Sounds quite reasonable, but need to test if it doesn't impact quality of photos took without attachments screwed (reflections due to screw thread, etc).

Could you point me to link for any "zoom objectives" with a screw mounting, of such small size, being widely adopted standard? Of course I don't mean those "magnetic" toys.

It will affect it totally - but it's not relevant here, as we'll be using same tricks for antenna reception, as currently implemented in any aluminum device (N950, iSheeps, etc). If everything else fails, we will just re-use antennas from standard backcover, and put them into non-metal, black "sockets" integrated into body - in a way, that will make aluminum body a back reflector for antenna.

/Estel