I think having both those working would be a serious reason for a lot of people to switch. E.g. just having working submodules and worktrees would do it for me.
Fingers crossed. Glad we're finally getting some viable Git competition with jj, Sapling and Pijul.
It does not implement Git worktrees, but instead implements its own notion of workspaces which frankly I find much nicer (unsurprisingly!). As with most things jj: just as much or more power than Git, but less hassle.
Working with submodules natively (see steveklabnik’s sibling comment for the “non-native” bit) will definitely be a big win.
Fingers crossed. Glad we're finally getting some viable Git competition with jj, Sapling and Pijul.