There is a hot thread on MTG Salvation's Card Creation Forum ( http://forums.mtgsalvation.com/showthread.php?t=166029 ) regarding bringing back summoning sickness. I argued that summoning sickness will never be brought back, but instead thought of an even better replacement called 'lag'.
For the formal rules on lag, go to http://shenafu.com/smf/index.php?topic=21.0 . Lag can do much more than summoning sickness, and I created some cards to prove that lag opens up very interesting design space.
Slowly rolling out Essence cards. Essence is card type similar in vein as Tribal in that it allows spell types to be put on permanents. The five major spell/essence types are the following:
Fractal conforms to pattern and uniformity.
Arcane uncovers secrets from the depths of the archives.
Psychic messes with players' mind and wins by emptying an opponent's library.
Entropy dumps everything into the grave, then removes them forever.
Force creatures and effects get bigger with things around them.
First cycle is wedge tri-color. Idea started with creating Jurassic Park for a Card Creating Contest (CCC) on GameFaqs, the