We've discussed the topic amongst the officers and we wanted to give you an update. Obelixa also posted this update in the legion invite list thread:
Legion enchants on gear is not mandatory at this time. But +850 gear should have some if they are not too expensive.
The same goes for flasks. Use Draenor flasks for now, if you can. Use legion flasks when the price comes down.
Gems +100 are easy to get. Ask a guildie like Obelixa for example to make them. Better is always allowed.
We'll revisit this topic at appropriate time.
Cheers and happy raiding and dungeoning!