This is just a short wee blog because I've had a mini-brainwave. I have a great idea for a seperate full-length blog which I will be implementing this evening hopefully.
In the mean time... Why couldn't WotC print cards that care about the rarity of other cards? How about something like this....
Common Sense 1U
Uncommon
Instant
Counter target common spell.
or
Rare Kill 1B (crap card name I know)
Uncommon
Instant
Destroy target rare creature.
Now I'm not a card designer or templater so apologies if there are any obvious mistakes here. And I know there are some small corner cases where you have a card which exists in two rarites such as Loxodon Warhammer or the like. I'm fairly certain the rules could be flexed to mitigate any problems such as Warhammer in Extended. Perhaps just make the official rarity of the card it's latest printing irrespective of the rarity of the printed card used? That's maybe not the ideal solution but I'm sure smarter peeople than me could figure a way round the issue of a very small subset of cards.
Is there something really obvious I which I am missing here? This kind of stuff has already kinda happened before during Kamagawa with 'Legend matters' cards.

I'm not really sure what I'm trying to do with this blog. I just wanted to put an idea out there and hear your opinions. It appears to be to be a completely untouched area of design space. Or have I missed a really small selection of cards from before my time? Let me know.
-Flame on-
Dave