@TheSeal: Ah, I understand now. You would like inexperienced players to be encouraged to unrated ("practise") games so you have a better chance of "equal" opponents playing faster.
While your suggestion might help a bit, it collides with the desire to have as many rated games as soon as possible in order to get meaningful ratings for better matchmaking (in regard to playing strength). Of course, the current ratings don't mean too much yet, and you're definitely right that there might be quite a large group of inexperienced players who have played mostly Base. The majority of these players will more often lose than win games with "new cards" and thus eventually get a lower rating, but if I understand you correctly, you are actually not referring to playing strength but to playing speed.
So a personal setting for "playing speed" would help you more, I think. You could set this to "fast", and inexperienced players (or players who like to think a bit more) could set it to "normal" or even "slow". That setting would then be considered in the matching process, possibly with a weight defined by the player as well.