Universal has notoriously only announced something months, weeks, or days prior to its opening. I'm sure they have their reasons.
As far as more stuff being added to Epic Universe... I think there will be some surprises as far as what attractions we see in the hub, but I think they'll be hyper focused on building high quality for the hub+their four main worlds they open with. Unfortunately, more often than not, stuff starts getting cut (due to budget and/or timeline) rather than the other way around.
Look at Animal Kingdom as an example.