The river Tiber (Tevere, Italy)
Made public on the 24/9/20.
Actually not the whole river (though this would be majestic), but a portion in Lazio, they say from Farfa
through Rome and till the sea. Not clear how much this would overlap with the historical centre of Rome, but it goes beyond that: they mention the bridges, Milvio and Sisto, the Tiber Island, imperial docks, naval dockyards from Testaccio to Marconi, the Cloaca Maxima (visitable by foot), down to Portus and ancient Ostia (wonderful archaeological site near the sea). It feels somewhat undefined, but still an autoinclude, principally because of Ostia, in my opinion.
They say they just started preparing the candidature and think that everything will be ready/will finish in three years (so not clear, tentative or definitive?), so I'm counting this as 2023.
Trivia: the 4th of October was the Tevere Day