I don't believe they've addressed if the mastery costs are also going up by a factor of 6.5, it's possible they'll still cost 500/600.
The relative value of 500/600 BE is certainly different now though (previously that 500 BE wasn't good for much except mastery anyway, but now you have to decide if you want the 500 BE, or save up for 6300 for the latest champ, or whatever other thing). Since many people were willing to buy multiple 1.7k IP champ tokens for the sake of disenchanting into essence to upgrade mastery though, if the prices remain the same, it seems like things will be cheaper relatively speaking.
And for that matter, if someone was willing to disenchant two shards (costing 3.4k IP currently) for essence anyway, if the new price is multiplied by 6.5 than it's still about the same as before, if not slightly cheaper.
That said though, champ shards themselves are supposed to be more common from the capsules we'll get from level ups, so using (mastery tokens+champ shard) instead of (mastery tokens+BE) might be a much more practical option in the new system anyway.