More intel on the new Paris-Vienna Nightjet sleeper train due to start December 2021: Initially 3 times per week, Paris Est dp 19:58 Tue/Fri/Sun, Vienna ar 09:50. Vienna dp 19:10 Mon/Thur/Sat, Paris Est 09:40. Will also serve Strasbourg, Munich Ost & Salzburg, but not Munich Hbf.

Potentially offers an easy connection from London by Eurostar with just a 10 minute walk between Paris Nord & Paris Est: London dp 15:31, Salzburg ar 07:xx, Vienna ar 09:50.

So London to Vienna using the Brussels-Vienna nightjet on Mon, Wed, Fri, London to Salzburg & Vienna using the Paris-Vienna nightjet on Tue, Fri, Sun.