I'd like for the legendaries to actually mean something. Back in the days of RBY, there were only 5, and Mew wasn't obtainable.
GSC introduced 6 more, and once again Celebi was not obtainable.
RSE introduced two unobtainables, and two separate trios. DPPt went over the top with 3 unobtainables, and BW was the same.
We don't need this many unobtainable legendaries. We don't even need this many legendaries at all!
I'd love to have five in total, possibly an event legendary for a 6th. Give us the two cover legendaries from the trailer, and the mandatory trio, and have one event legendary. Any more than that is really just unnecessary.
And if my dream that these games will be incompatible with Gens 3-5 comes true, then there will be events for all of the past unobtainables anyway, so there's no reason to have 3 additional ones.