It's the end of the expansion ( like timeless, argus, etc... ).
The new cap will be 425 ( the actual ) +30 = 455, so a 430 openworld is not a big deal ( also they would like to see the zones with many players ).
Currently with emissary and world quest you can achieve the same ( 400 out of 425, which has the same gap ) with timegate, but with a chance of warforged/titanforged, which can be better than ilvl 400.
Also remember that probably you will still have to do emissary or mythic or raid in order to collect azerite pieces, because there's a probability that head/shoulders/chest you are going to drop on the island won't have azerite traits. We will see.