I don't know why the over rate is now allowed to drop so far. Allowances are one thing, but there seems to be no will to do anything about it. There will always be some delays with reviews, head hits, etc, but that should be fairly obvious rather than reviewed after the match and without much public notice.
Subs I have some problems with as they have been abused by quite a lot of sides, hence the limitations now. Flintoff used to bowl 5 overs and then go off for a 20 minute massage - an absolutely deliberate abuse of the rules.
I do agree that the players won't be able to keep up longer days - just make it 90 overs again, by 6.30 in England.