what are some of the legal exemptions? living in the US?
Medical exemption, or if one didn't reside in Israel for more than 6 months (per year IINM) after a certain age (12 IIRC, but it can be looked up).
No one suggested you cannot permanently return to Israel, rather what was suggested was a cooling off period; I don't see even if true how a temporary cooling off period would be a deterrent to renouncing
So let's play out that suggestion:
Someone renounced their citizenship, and the next day after approved, fly to Israel with foreign passport (and certificate attesting that Israeli citizenship was renounced). They check in with the airline at US or EU airport with US or EU passport. Nowhere on the airlines terminal does it say that they have to ask each passenger if they are or were previously an Israeli citizen. They arrive at TLV, stand on the line for foreign passports, hand their passport and certificate attesting that they are no longer an Israeli citizen, and what happens next??