You're right, this would really alter the dynamics of a PhD. As is, it takes ~2-3 years since the end of experiments and beginning of writing of an article until the that article is actually released and printed. Granted, this varies by field a tremendous amount, but lets just call it ~2.5 years of 'publication hell' on the average for an article. If you were to add into this the need for confirmation, you are adding in not only the time it takes to re-run the experiments, but also the time it takes to draft them up and go through another shorter round of 'publication hell'. Lets call that 6 more months of experiments and 6 more months of publication hell. Then you have ~3.5 years of sitting on the data and the experiments since you last touched the bench with that experiment.

Many PhD programs have requirements for the number of first-author papers you must publish to get your degree. I know of one that requires 3 first-author papers to graduate, granted a little high. Running with these very loosey-goosey numbers: Say your experiments work well and only take 6 months to preform. That's then a total of 4 years just for the first paper to get out, no sooner. As you are working on the drafts, you also preform another experiment immediately after finishing the last one , so lets call it 9 months for the added time it takes to get the last one typed up. Now we are at 1 year and 3 months with 2 successful experiments and some progress of getting the first experiment into publication. Lets do that again, and you are at 2 full years and some progress on your first and second papers. That means at a minimum, you then can get out of grad school, with the new confirmation studies to do, at ~5.5 years out. That is not too bad, right?

Now what happens when that first study was not repeatable and you have to start over? That means you have to do another experiment starting the ~3.5 year process all over in your 4th year. Now we are at 7.5 year total. What happens when the last experiment is non-repeatable? You have to do another experiment starting at year 5.5, for at total of then 9 years in grad school minimum. And yes, you can be trying for 4th and 5th papers this whole time, lessening the time in school, but each also has some chance of failure.

And this is only if you are running experiments all day and they only take 6 months total to do successfully, even the repeats and new studies that don't fail you more than once; the re-do of the last one is successful and also does not fail.

Yes, these number are a bit out-of-the-hat, but I think we can all see that the length of stay in grad school either must increase by a lot, or the required number of papers must decease by a lot, if they are to be required at all. Either way, you are not getting much education while some lab elsewhere (maybe your competitors) is sitting there trying to replicate your experiments with some unknown amount of success or efforts to do so and you are just waiting and praying that you don't get screwed into a decade of grad school.