The append-only file just... well... appends every command to a file. That's pretty solid, especially on journaled filesystems, so I can't find any durability-related reason why it shouldn't be used.
The only durability "problems" I've ever been able to come up with for Redis involve human error as a key component, like what Twilio experienced here with the AOF/RDB mixup.
The new CONFIG REWRITE command makes it easier to avoid, but it would be nice if it were harder to get this wrong in the first place.
What it definitely isn't is fully ACIDic, though for some workloads you can get close if you use it very, very carefully.
Postgres has had it's failures under weird confluences of circumstances - and learnt from them a decade or more ago.
I would like to see Twilio standby their stack choices, invest time and effort and sponsorship of redis so that in a decade or two people will be taking it on faith that redis is bullet proof (well the combined postgredis datastore:-)