Personally I think 30 years from now the safety systems and gear we have will be even more advanced; just like car seats, cribs etc from a generation ago are now considered totally unsafe, due to both age and outdated design, the same will be true in the future.
No doubt school buses today, even without seat belts, are far safer than they were in even the 1970's. In my kindergarten years, 1982 through 1984, our old mid day bus was a van style mini school bus, not equipped with a stop arm (although the newer ones then had them), and although it had lap belts EACH SEAT HAD ONE LAP BELT TO GO ACROSS BOTH KIDS!
But no doubt it was an improvement over 1960's buses with hard metal seatbacks to "compartmentalize" into.
But yet even one death is one too many..a child in our city died a few years ago in a bad school bus accident on the espressway.
No doubt with lap and shoulder belts there would have been zero serious injuries; the bus just rear ended a semi and bounced around very badly but there was no space intrusion and no rollover.
But the vast majority of children killed as a result of school bus accidents are killed when they're run over by the bus..usually their own bus. Money is always limited and choices have to be made. Perhaps an adult bus monitor on each bus might be a more efficient use of limited funds, in terms of deaths prevented; someone that can disembark with the children, get down to check that nobody is crawling under the bus to pick something up?