so all of those suggestions are pretty much the accumulation of the diagnostics.
before going forward, connection issues can be caused by distance and obstruction. make sure any paired devices are not blocked by things such as doors/walls of an entertainment unit, walls, or couches, or even the human body.
1) i always start with a factory reset, and firmware restore. download the PS4UPDAT file from the Playstation website, and reinstall it onto the device by following the steps supplied by sony's support page. The reason i start with this, is because it is the least invasive of the repairs, and fixes a various number of issues that are caused by data corruption.
2) Next, i would look at a cleanout. Dirt and dust are conductive, and can cause board shorts. this can cause issues with processing the components like antennas.
3) replacing internal components. the Pickups for Bluetooth and Wifi are wired through the device, and mounted into the front of the housing. they can pinch from just moving the device. they can also build up static electricity from dirt and dust in your device, which could essentially damage them if the discharge is powerful enough.
4) Logic Control for the Wireless device: The wireless card is soldered into the motherboard, and replacing this requires a skillset in Surface mount Soldering. this could be failing, which can result in faulty connection.
5) Integrated motherboard failure: The problems could persist into the circuits in the board. this would require a board replacement, and that becomes more expensive than replacing the device itself, as the board is also paired to the Disc drive, which would also need to be transferred.