An unpopular opinion, but i feel like if we do see KF1 maps from Tripwire, it should be an "after the end" scenario rather than just "Old maps with a new coat of paint" (KF1 manor would probably just be high res textures rather than a new aesthetic. I think the following maps could work:
Biotics Lab Classic: Art assets from KF2 biotics lab super-imposed onto KF1's map layout
KF-Offices: Newer computers, building refurnished and clean of blood (only to be covered in blood by the player).
West London: Now a military base run by Kevin Clamely. Patriarch replaces the Trader
KF-Farm: Dead cows replaced with Husk containers, all non-residential buildings renovated by Horzine, Patriarch replaces the Trader
Clamely Manor: New textures and models. Dunno how you'd do an "After the end" scenario for Manor.
Evil Santa's Lair: Yes, i know it's not a Core Map in KF1, though i think it's worth including due to being the OG KF1 event map. I imagine some art assets from Biotics Lab and Containment Station would be used, albeit with Christmas zeds stuffed in containers