looking at this from another perspective, would a further reduction possibly see an increase in injuries or in the long term players having shorter top flight careers due to burn out?

I think otherwise. The fatigue factor would probably mean the average impact on players up the middle be a little less.

Indeed. There'll be fewer fresh props around bending people in half.

The flip side of this is that half fit players are less likely to be played or put on the bench as there is more chance
of leaving your team short.

A step in the right direction but not nearly enough. I'd have unlimited players on the bench, with no more than 4 tactical substitutions but unlimited injury substitutions, with independent medical examiners assessing players brought off injured after the game with massive penalties applied to any team trying it on (except Wigan and Leeds of course - we'd have to come up with ad-hoc rule changes when necessary to let them off any infractions naturally). RL desperately needs to up it's flair, skill level and spectacle to survive and getting rid of the one-dimensional 20 minute bargers from the pitch and letting the halves and backs have more room to breath needs to be the first priority, and severly restricting substitutions is the only way it's going to happen.

You can see this kind of rule change benefiting more mobile packs. The fekas of this world would struggle without there regular 20 minute break. Maybe it was all a secret plan by Royce last year to get us ready for this year with his lack of using a sub.

The genius starts to show