Maybe something like this:
$ wp plugin list --format=csv --fields=name,version | awk '{if ($1 != "name,version") print $1;}' | awk -F',' '{system("composer require wpackagist-plugins/" $1 ":" $2)}'
Note: It actually run $ composer require
for each plugin
Update:
maybe this version, copy and paste the console output to composer.json
$ wp plugin list --format=csv --fields=name,version | awk '{if ($1 != "name,version") print $1;}' | awk -F',' '{print "\"wpackagist-plugins/" $1 "\":" " \"" $2 "\","}'