Will BW4 hana Replace the conventional BW system since both modelling and reporting can be attained through HANA - Powered by Fiori Apps?

YES, BW is legacy system now and BW4 HANA is a very advanced and rapid data analyzer from cloud data to Hana to produce the reports in few mins time. It works well in and one can customize their reports as per their needs, also it provides the flexibility to work with Fiori and other systems through interfaces.

Yes, especially because of fast response time and its flexibility to integrate with frontend reporting tools