At the pre-patch PTR and first few weeks after 7.0 went live loot in both EN and NH was 850 / 865 / 880. Though, they've written in the tweet that the gap will be like between HM and BRF. One can guess, loot in EN can go up to 890, that's why they did Mythic NH loot 905. I don't think anyone will be full 890 prior to NH release, so it seems an extreme overkill to me.
Then Stormheim should be 6 bosses at least. I wouldn't consider it 'small' in this case.