There is the capability to configure Service ExternalIP for the ingressgateway on the smcp CR but the service is not created accordingly, because the service template used by the operator is missing the parameter in case smcp has it configured.
Some customers might want to use this feature in Openshift and on some ingressgateways, instead using OCP routers.

https://github.com/maistra/istio-operator/blob/maistra-2.2/resources/helm/v2.1/gateways/istio-egress/templates/service.yaml

Example:

oc get smcp -o yaml:
gateways:
ingress:
enabled: true
runtime:
deployment:
autoScaling:
enabled: false
service:
type: ClusterIP
externalIPs:

• 172.23.189.6
  ingress: true
  appliedValues:
  istio-ingressgateway:
  autoscaleEnabled: false
  enabled: true
  externalIPs:
• 172.23.189.6
  gatewayType: ingress
  ior_enabled: false
  name: istio-ingressgateway

We should perhaps have:

spec:
{{- if $gateway.externalIPs }}
externalIPs:

• {{toYaml $gateway.externalIPs | ident 4 }}
  {{- end }}
  {{- if $gateway.loadBalancerIP }}
  loadBalancerIP: "{{ $gateway.loadBalancerIP }}"
  {{- end }}
  {{- if $gateway.loadBalancerSourceRanges }}
  loadBalancerSourceRanges:
  {{ toYaml $gateway.loadBalancerSourceRanges | indent 4 }}
  {{- end }}
  {{- if $gateway.externalTrafficPolicy }}
  externalTrafficPolicy: {{$gateway.externalTrafficPolicy }}
  {{- end }}
  type: {{ $gateway.type }}