Learning SAP HANA and scope with ABAP-HANA or BI-HANA

While you have a valid point that most of the SAP HANA projects are coupled with varied SAP landscape but there does exists a lot of projects which involve only native SAP HANA development.

It entirely depends on your interests and knowledge base but sound understanding of the core concepts around data ware housing needs to be clear, if you are planning to build anything utilizing the base concepts.

Presently, as per my understanding, clients prefer ABAP on HANA as they have one or other existing ABAP solutions. So, any enhancement using ABAP seems more sensible and appropriate.

So I will suggest you to go the OpenSap.com and go through few of the free courses available to understand the concepts better and clear.