I agree that fatigue could be an issue with RP07 although probably no more than with the fallback and at least this fact has been recognised and a couple of tools have been introduced to alleviate the problems.
At para 16.4
"other than in abnormal circumstances, crew members on reserve duty will normally be notified of a callout as soon as is practicable"
This has 2 expressions that I hate to see in such a document: "other than in abnormal circumstances" and "normally", both possibly subject to abuse. However, my experience so far is that we normally do get good notice of a callout and it's important as we move forward for everyone to flag up to the JRC when they're called out late so that the controllers are kept in check, neatly bringing me to the other tool used to alleviate the possible fatigue issues: The existance of the JRC. A sensible liasion between the pilots and the company regarding rostering has never existed in Cx before. This is a big step forward and something that we need to keep going.
In reality I think that the new reserve scheme is less tiring. If you've a 4 hour evening reserve to cover the long hauls for say 4 days on the trot, are you really going to have a sleep every afternoon just in case, thereby messing up your own body clock, call out or no? Probably not.
I'd rather have the 12 hour reserve with a commitment to let me know early if i'm going to be used, but I do realise this is just my own personal preference!