You missed a word, it says:
any excommunication, suspension, interdict, or other ecclesiastical impediment".
No. I didn't miss the word. It would not change the meaning of the sentence. If the cardinal had become a Lutheran and was thereby excommunicated, he would not be welcomed into the conclave. If you believe he would, then you are willfully blind and all Christians are called upon to simply shake the dust from their feet.
It does change the meaning of the sentence from the meaning you gave it. Your claim that because it did not mention the word "heresy" explicitly, that heresy is not included in the decree - it's either that or you don't believe that heresy is an excommunicable offense - which I highly doubt you believe.
When you add the word "any" to "excommunication", that word makes the decree all inclusive, inclusive of all excommunicable offenses without distinction, which therefore necessarily includes heresy whether you believe heresy excommunicates one or not.
So here we have popes who make it a law that no cardinal can be excluded from the conclave that elects the next pope, that IF any Cardinals are under any censure, whatever the censure might be, the censure is suspended only for the election.
"We, in fact, suspend these censures only for the effect of an election of this sort; they will remain in their own force in other circuмstances...."So presume that no one knows that there are 10 heretic cardinals in the conclave because they are secret heretics who have vowed within themselves that if elected, they will misuse and rob the Church of her riches, appoint heretic cardinals and bishops, in short, he vows to use his authority to destroy the Church.
The question remains - what is there to stop the conclave from electing one of these heretics as pope?
Now, you can answer a million times that if the one who gets elected is a heretic, that he is not the pope, but that does not answer the question.