Hi Valentin,
Not sure if it's still relevant, but i was also looking into this topic and here are my findings.
I don't know why the class was set as final, but you can copy it into your own one. Then you manually assign it as a handler for your ZBSPWD_BASICS\ErrorView2.do.
But I fear this is not enough and you need to check that your view is called as it's hardcoded in CL_BSPWD_BASICS_WA_HOST_VS=>GET_VIEW_AREA_CONTENT_ID of BSPWD_BASICS/WorkAreaHostViewSet.
Also it can be useful to check that all controller substitutes are OK: see view cluster (sm34): BSPWDVC_CMP_EXT;
You can also try to develop your component/application and use it in the runtime profile: BSPWDV_RF_PROF_C;
Please let me know if it helped. I did not try it myself yet.
Thanks and Regards,
Dima