A few days ago I joined a conference on SAP S4/HANA Conversion in St.Leon-Rot, Germany. Unfortunately, there is only a German description of this event available, but I will share my summary and thoughts on the event here with you.
SAP S4/HANA Readiness Check - Note 2290622 (Raphael Maultzsch)
The tool is implemented via SNOTE into the ERP system. Readiness check regarding add-ons could be done in DEV system, complete readiness check should be done in PROD or copy of it. It also includes sizing recommendations for a future HANA system. Business process analytics checks for open (FI) documents which will cause problems in a potential S4HANA conversion project. ST-A/PI needs to be 01S (SP2/SP3).
If you have enterprise support subscription, you can consume the Readiness Check as EGI.
Report /SDF/RC_START_CHECK provides an up to date list of simplification items and checks if the items are relevant for you, by checking the usage for certain table for example. Note 2399707 is the one to go for. This one is depending on 2502552 if you want to use the check at its full scale, as a check for 1709 requires this note to be implemented as well. For the later note, it is helpful, but not necessary, if the SAP Download Service is enabled on your system.
In general, a lot of things can and should be done before the "S4/HANA conversion Project", for example, Customer-Vendor-Integration (CVI), if you do not use the Business Partner, yet. Check the CVI cookbook.
Custome Code Adoption (Olga Dolinskaja)
Adapt custom code using Simplification DB (transaction SYCM, see note 2241080 & 2185390)
To be able to implement the above-named notes necessary for the SAP Readiness Check, transaction SNOTE has to be enabled for TCI (Transport-based Correction Instructions). A documentation on TCI is attached to note 2187425.
Moreover, it is helpful if the SAP Download Service is enabled. Relevant notes are 2576306 and 2554853.