I know that POS was (and still is) the plan all along for ETH, but I don't know why they cannot come up with some type of hybrid system, say 50% POS and 50% POW.

Some coins are now even going POUW (Proof of useful Work), so maybe some type of change in that area, say 50% POS and 50% POUW, since one of the main arguments for the switch to pure POS is to reduce energy consumption.

Myself I never was a fan of the POS concept in that is it simply bringing the normal financial system to crypto, mainly in that the reward goes to those with the most tokens (money). While POW is far from perfect, I am sure if efforts were focused into this area improvements could also be made to help reduce energy consumption and pretty much eliminate the useless work while still maintaining the decentralization benefits.