Hi Manish,
The existing name is more suitable for configuration where the platform has BL1 in it and BL2 can run at EL3 instead of S-EL1.
Well, that is a minor thing to take care. V9 implementation does that in a way.
This configuration is currently not available in TF-A but having this flexibility is not a bad idea and it can be platform's choice.
That's my answer! And the default choice costs some memory with probably no increase in security (V8).
BL31 can mask the secure world.
Cant be done reliably on V8 (with root world V9 or EL2_S there is potential to compartmentalize the secure services as PAS isolation is feasible) Ex: EL1S can always overwrite the BL31 Xlat tables and take control of the vectors and many other ways depending on the platform. It's the same PAS!
Thanks Sandeep