Agreed, they're no longer in a position where they can dance around a IP like that. An with anthology houses, if it's IP-based, they're better off using IP's they own to avoid any issues. For me the Classic Monsters are honestly the best fit for that, so Silver Screams with them would be great. On the flipside, houses like H.R. Bloodengutz and Slaughter Sinema are great settings for any original creations. (Now I've seen some people clamoring for both a H.R.B. and SS sequel for 2019, but considering both are right in the campy side of horror, I'd say just one or the other since they'd be way too similar together.)
As for the UCM being held off till the 30th, for me it's hard to say. It all depends on what kind of direction they'd want to take it in. XX was more about ushering in a new era, so the houses were more new ideas. If XXX is more about looking towards the future, I don't know if they'd use the UCM that much. However if the direction is celebrating the past, then I'd be inclined to agree they'll be using them.