I hereby update my own article for the possible update paths I see just by looking at wikipedia.
It’s important to point out that I care more about the “blob list” (the stuff one cannot get) and about the ideas how the fairphone project will ensure an ongoing software support.
Also I would like to know more about details on how all this is communicated with the OEMs that themselves are only buyers/licensed for the SoC, that itself is bought/licensed together.
Possible update/alternative OS/software pathways (based on Snapdragon 801 support, see links below)
Snapdragon 801 -> Android
Snapdragon 801 -> Android -> Fairphone UI
Snapdragon 801 -> Mer -> Sailfish OS
Snapdragon 801 -> Nemo
Snapdragon 801 -> Tizen
Snapdragon 801 -> cyanogenmod
Blob list (based on Snapdragon 801 support, see links below)
There is open source support for the WiFi wireless and the graphics module for the SD8xx.
Possible future hardware updates
There could be snap-in replacements for the SoCs (SD801, 805, 808, 810 … 820), that would include upgrade paths to newer Android versions and other hardware upgrades.
Risks
Pro: Good for people that want the latest Android versions and experiment with other os software for a longer time. Lots of software possible supported, if given access to all the right blobs.
Cons: Binary blobs, Licence changes with newer SoCs and more blobs, still Qualcomm. I also assume that the full board will have to be exchanged for upgrades (DDR3->DDR4, eMMC).
Links (OS)
x https://en.wikipedia.org/wiki/Comparison_of_mobile_operating_systems
x https://en.wikipedia.org/wiki/Mer_(software_distribution)
x https://upload.wikimedia.org/wikipedia/commons/1/1b/Mer_and_mobile_operating_systems.svg (overview picture)
Links (Hardware)
x https://en.wikipedia.org/wiki/Adreno
x https://en.wikipedia.org/wiki/Qualcomm_Hexagon
x https://en.wikipedia.org/wiki/Comparison_of_open-source_wireless_drivers
x https://en.wikipedia.org/wiki/List_of_Qualcomm_Snapdragon_devices#Snapdragon_801
x https://www.qualcomm.com/products/snapdragon/processors/801
x https://www.qualcomm.com/documents/snapdragon-801-processor-product-brief (PDF: easier to read)