I own a 600D and what prevented me to go for 5DMk2 was the lack of built in flash.
So for a hobby user, not sure the 6D is versatile enough without flash for fill in.
I don't understand why Canon think flash is only for dummies
that´s something i never cared much about.
it´s my least concern with the 6D.
i never used the popup flash.
only usefull thing (for me) would be as trigger for other flashes.
ok you could do some fill flash with it.
but to be honest whenever possible i have a speedlight with me (at least one).
but of course i see the usefulness for people who are not such strobists like me.