ok, so was listening to this episode and you could open a channel in one transaction if you coordinate offchain first.
From about 29:45
TFTC: A Bitcoin Podcast: #431: Bitcoin Privacy and the Payjoin Dev Kit with Dan Gould
Episode webpage: https://podcasters.spotify.com/pod/show/tales-from-the-crypt/episodes/431-Bitcoin-Privacy-and-the-Payjoin-Dev-Kit-with-Dan-Gould-e26ddq4