I’ll just mention Foomuuri here. Its bit of a spiritual successor to shorewall and has firewalld emulation to work with tools compatible with firewalld
Foomuuri is ALMOST there.
I mean there are some payload over payload like GRE VPE/VXLAN/VLAN or IPSec that needs to be written in raw nft if using Foomuuni but it works!.
But I love the Shorewall approach and your configuration gracefully encapsulated Shorewall mechanic.
Disclaimer: I maintain vim-syntax-nftables syntax highlighter repo at Github.
Thanks! Would be cool to have it packaged for alpine since firewalld requires D-Bus. There is awall but that's still on iptables and IMO at bit clunky to set up.