What feature/behavior/change do you want?
Need a way to attach multiple Additional Security groups, Currently vpc.securityGroup only support one SG.
Why do you want this feature?
I work with customers who uses multiple security groups to control their traffics. Here when we create cluster using eksclt, vpc.securityGroup setting only allow to specify single security group where as CreateCluster API or EKS console allows you to choose multiple security group. This makes eksctl tool less likely in situation where multiple security groups needed by customers.