im not so sure i agree with that. reverse time takes things into the past, but yet undead cards get taken into the past when it is used on them. its just not in the standard defined use of reverse time.
i can not come up with a good example for rage potion, but it is in the realm of possibility that a card could be targeted with rage potion and then have an effect other than the +5|-5 and still thematically be made angry. i dont think it is a good idea to exclude cards right now just because at this moment we are unable to think of an application for it. it just makes it less likely that someone will come up with a card, or cards, which utilize this particular spell/effect/status/ability.
ok, very basic and not well thought out off the top of my head example of a card which would use rage potion differently than its intended effect
Pixie
3
3|3
Pixie turns into a Nixie if targeted with Rage Potion
Nixie
3
3|1
Momentum and Adrenaline
or simply be a nixie from the start and again momentum and adrenaline upon reviving a rage potion. while this may not be the most creative idea, the goal is to allow for the possibility of creative thoughts even if we do not have them at this moment.