Hey, Zadok, I have seen many newbies with Portal cards walk into tournies as it is now. Every few weeks, we have some kid walking in trying to play his Portal cards in the tournaments. If it's legalized, he may be confused, but at least he won't be completely pissed that all of his cards are useless.
And really, most people won't go into the tournaments with their Portal cars anyway. Most of the kids above have decks that are half regular cards and half Portal. Most of them have a rudimentary understanding of timing and stuff, they just don't know that they can't use their Portal cards.
Most people learn from their friends; it's not that often that they learn by themselves. And those friends will tell a person that they aren't ready for a tournament.
And finally, most people get slaughtered when they first start in tournaments anyway; kids with Portal will just get slaughtered while playing with Portal cards.
In my opinion, it's wrong to try to get people to buy these cards to start the game, and then tell them that they can't use them and they have to buy more. It's like getting someone to buy a chess set, and then tell them that they can't actually play unless they buy another one (okay, that wasn't the greatest example, but it was the first one that popped into my head).
An alternative would be to make Portal more like regular Magic, just with less complicated stuff. Instants are a pretty easy idea. Clone and Saproling Burst are not.