Found a config to ignore lockfiles system-wide:

package-lock

• Default: true
• Type: Boolean

If set to false, then ignore package-lock.json files when installing. This will also prevent writing package-lock.json if save is true.

When package package-locks are disabled, automatic pruning of extraneous modules will also be disabled. To remove extraneous modules with package-locks disabled use npm prune.

This option is an alias for --shrinkwrap.

npm config set package-lock false

cc: @dominic is this something you'd fine helpful?
I think diffs can be ignored too:

# one-off command
git diff master -- ^package-lock.json

# global config
echo "package-lock.json binary" >> /etc/gitattributes