It's very antithetical to that goal to add more layers of abstraction that could be buggy or reduce security. We're talking about motivated and intelligent people purposefully trading off convenience for security.
Containers, btw, cannot be snapshotted. So that's a weird thing to put into your question.
They've also discussed booting UEFI directly to VPN nodes: https://mullvad.net/en/blog/2022/1/12/diskless-infrastructur...
It's completely weird to argue that they might introduce a layer of insecurity here. Directly goes against everything else they're working on.