Promising things in the rebuttal phase of a review
Rebuttal phases offer authors an opportunity to swing the opinion of reviewers. To swing the opinion of a reviewer, authors must present convincing evidence. If a reviewer wants more experiments, then it is (IMO) reasonable for authors to promise them. However, that won't swing the reviewer's opinion. To swing their opinion, authors need to convince reviewers that the additional experiments can be added before the camera-ready deadline. That is, authors must show that these experiments can be conducted quickly.