> attackers have effectively infinite time

No, attackers are also rational economical actors. They don't randomly attack any software just for the aesthetics beauty of the process. They attack for bounty, for fame, for national interest, etc. No matter the reason it's not random and thus they DO have a budget, both in time and money. They attack THIS project versus another project because it's interesting to them. If it's not, they might move to another project but they certainly won't spend infinite time precisely because they don't have infinite resources. IMHO it's much more interesting to consider the realistic arm race then theoretical scenarii that never take place.