What are the chances of an article to get published if it got minor revision comments, and a single optional major revision comment? Our paper have been reviewed two days ago. The comments of the the two reviewers are few and of minor type (spelling and format issues) and can be addressed easily, except of one comment in which one of the two reviewers "optionally" asked if we can use data from other locations. However, we cannot do this now. Getting the data will take long time before being used in the study, the deadline of the journal revision is so tight, and the study is already intense and long. The status on the journal online system is "Major Revison" despite the fact that all other comments are minor, and the only major comment is optional.
How do we respond to the reviewer to take the other option: not adding new data?
What are the chances of accepting the paper in this case?
I have had this on a couple of papers. When I first had this, my advisor at the time told me that this is not usually something to be overly worried about and that it presented an opportunity. Specifically:


It is optional, as @FuzzyLeapfrog said in her comment:



  Thank the reviewer, let him know that you are aware of the benefits of using data from other locations, add a paragraph on this in the outlook part of your paper as "future work to do" and mention this in your response to the editor/reviewer.


It is also important to state in your 'response to review' document that the time taken to obtain the additional data will be prohibitive.


Additionally, take this optional revision as possibly the impetus for you to do another paper based on the suggestion.


In regards to the editor's decision of 'Major Revision', reread the message to check to see if this optional revision is in fact the reason. If in doubt, be sure to make contact with the editorial team to clarify.