Nice addition gives a lot of flexibility in GCP, 

I have a customer who I have helped deploying firewalls behind GCP iLB (internal LB) and set the next hop to the iLB. They are using Interconnect (Dedicated) no the IPsec tunnel for accessing on-prem.

Would you consider another topology where iLB as the next-hop is used as an extension of 1a and 2a as a supported method?