Actually 48V mild hybrid may not be the best name. Some suppliers like Continental are calling their upcoming P2 48V as full hybrid.Magna concept looks promising - I believe competition is working on similar.
My take is: 48V mild hybrids - which is current definition/status -will only give very limited fuel economy gain, and unsatisfactory e-drive.
Maybe P0/BSG 48V tech have already tarnished 48V hybrid reputation.
For example here is data for the 4th gen ZF 8HP:
PHEV up to 160KW at 350V, MHEV up to 34kW at 52V
Just for comparison this is for the 2nd/3rd generation:
Electric motor with a maximum output of up to 40 kilowatt (Mildhybrid: 15 kilowatt) and maximum torque of up to 230 newton meter
So low voltage hybrid will catch full hybrid in few years. Even ZF is skipping full hybrids or let's say high voltage hybrids in the next generation and will offer only mild hybrid (low voltage) and plug in hybrids.
FCA made the order for the 4th generation ZF 8HP.