We have not upgraded and are trying to avoid it as much as possible. We are doing that by separating out non-core modules such as HR, CRM, etc. to narrow the footprint in case we decide ultimately to move to Hana. I've not had much luck with any of the big SI’s and would try to use folks like Cognizant or TCS instead.
We upgraded our SAP Business Warehouse environment from Oracle to HANA database last year. Plans were made to upgrade core SAP ECC to HANA, but dropped. Thought process was to evaluate S/4 HANA migration in few years to avoid duplicate testing and effort for ECC Migration. Quite a few boutique firms can help in this effort.