Why are you suggesting HCI (GaaS) ?
Here HCI acts as your front end Gateway system communicating with OData services. This would give us a confirmation before setting up front end server 7.4 / 7.5 as per the requirements and that backend business suite is n't disturbed..
Its always good to make IW_BEP = SAP_GWFND (frontend)
GaaS primary purpose is to eliminate the maintenance of front end server and immediately start integrating OData services in new fiori apps via Hana Cloud .
Hana cloud services (one among is HCI) would definitely open new doors of innovation via HCPMS, IOT and many with lower infra maintenance
Yes , we still need IW_BEP in backend for both GaaS and HUB deployment scenarios.
From what i see in HCI , the development happens in Backend system.
Regards
Virinchy