It's not. All 3 have an internal ONU and until now no compatible 10G-EPON ONU has been found on the market.
However all 3 support a bridge mode, which makes them (power consumption apart) almost the same as an ONU.
this is sad to hear, having a high bandwidth plan only to be limited by mandatory hardware... oh well, thanks for giving me closure on several weeks of searching and asking around, I did find it weird that there is no documentation available on how to replace a freebox with a custom router.
hmmmm, I wonder, if I request for it, would they provide one of those "boitier fibre" that other ISPs have between the wall and the box ? (Unless those can't do SFP+ speeds, in which case it makes sense that they didn't get us one in the first place)