Google translator loses a lot of information for non-french speakers like me, but I don't want to start another "international thread discussion" here...
Without completely understanding the whole discussion I want to participate and tell you my experience:
8Bitdo SF30 Pro controller works fine in switch-mode (Start + Y) on xmas-beta and Pi3 B+' internal bluetooth here.
I use Start+Y, because in this mode the controller shuts down as soon I shut down recalbox. - Like also Sony DualShock 4 controller does by default.
Also 8Bitdo G. Bros adapter works perfectly in switch-mode.
In conclusion: No issues here. And I guess there will also be no issues in Android mode (like @Scavy said)
I just have troubles with these 2 recent 8Bitdo controllers (in ANY mode) with latest recalbox stable + CSR-based bt dongle + Pi3 B.
But that's another story Anyway, this is just the main reason why I'm really looking forward for the final Pi3 B+ version, where I dont't need the bt dongle anymore. Beside 5G wifi and maybe a bit more performance. Not so into having more emulators, just looking for support for the better hardware