Hi Deepak,
If you have a BW on HANA environment, you should be able to get a lot of the underlying benefits already for the data flow you have mentioned & then connect BO via BICS. If that option doesn't suffice your requirements, starting SP08 and HANA Rev 37 you can import BW cubes & DSOs as calculation/analytic views within HANA (via the HANA studio) and connect your BO reports directly on it.
Alternately if you have to migrate the entire flow to stand-alone HANA for other reasons, I can think of the following options:
a. With DXC, you could extract data from your custom datasource in ECC and then incorporate your transformation logic within analytic views and calculation views. More complex transformations can be embedded into a script based calc view.
b. If you have BO DS, you could extract from a BW extractor (you need to check SAP Notes to see how you can enable custom datasources to work with BODS) and then embed all your transformation logic within data services before pushing the data into a HANA table.
c. You could use a combo of (a) & (b) - extract using DXC into HANA tables and then use BODS to run your transformations. BODS can take data from HANA tables, tansform them and write them into another set of target tables within HANA on which you can create your views.
Needless to say, the options above must be assessed based on factors such as licensing, performance, maintenance, TCO etc.
Hope that helps!
Thanks,
Anooj