It will undoubtedly include Pavé and a redesigned Pavé series. I really enjoyed the new version of the harvest festival set, so I hope they'll do a similar job with Pavé's. I don't know if Brewster will be a part of this update... Honestly, I don't think we'll see him before March or April.
It seems likely to me that we will see some new ways of designing your island. It would be nice to see new kinds of default paths on the Island designer app. I personally long for a way to customize cliffs and riversides, as it is imagined in this Twitter post from a while ago.
In my opinion, it would revolutionize the way my island looks.
However, house exteriors customization is much more likely to be included in a future update such as January's. Maybe we'll be finally able to live in a manor or in a Japanese castle, like in New Leaf. If they included such a feature, they would probably add new customization options, maybe with other architectural styles.
OMG you spoiler, i need that i it looks so pretty i wanna do that to my hills and river sides