So is Germany looking at putting forward Herrnhut (the center of the Moravian church) as an extension, or are they just looking at supporting the planned extension of the Danish site to the US?
The initiative apparently came from Bethlehem. According to this news, they wrote a letter to Herrnhut in March 2021 to suggest a transnational nomination. Gracehill in Northern Ireland would also be part of the nomination.https://www.mdr.de/nachrichten/sachsen/bautzen/goerlitz-weisswasser-zittau/welterbe-bewerbung-herrnhut-100.html
Germany is currently working on a revision of the T-list for 2024. But given the fact that Germany nominates at least one site every year - and does so very successfully - I guess it is unlikely that it will take the leading role here, although it would be logical, from the historical perspective.
On the other hand, I don't think it would have to compete with another US proposal. The US will certainly not nominate one site every year in the future. And one year more or less would not make a big difference for this transnational proposal.