Everything I've read about btrfs's RAID5/6 deficiencies is that it can't tolerate sudden losses of power (aka write hole problem), which I think is fine so long as you are aware of it and implement appropriate safety measures such as a UPS or APU.
And besides, if you are doing RAID you are probably concerned with the system's uptime which probably means you will have implemented such measures anyway.
Note that, yes, I'm aware most home users either aren't aware (nobody RTFM) or are too lazy/cheap to buy a UPS from Office Depot. So perhaps btrfs is warning people to save them from themselves.
A UPS will not much improve the reliability against sudden power loss. At least here in Europe it is much more likely that a PSU or other component fails than that the power line is suddenly interrupted.
And lost writes are a problem that all filesystems have. I recommend reading the paper "Parity Lost and Parity Regained" by Krioukov at USENIX 08...
And besides, if you are doing RAID you are probably concerned with the system's uptime which probably means you will have implemented such measures anyway.
Note that, yes, I'm aware most home users either aren't aware (nobody RTFM) or are too lazy/cheap to buy a UPS from Office Depot. So perhaps btrfs is warning people to save them from themselves.