If the volume of citable items during a two year period increases at a fast enough rate (instead of remaining fairly constant as it normally does in a regular journal that publishes periodic issues with a fairly set number of articles per issue per year), then the impact factor is likely to decrease simply because there is a greater dispersion of articles to cite. This is further complicated by th...

I think "complementary" is a typo. Do you mean "praised the SAGE Open and PLoS ONE review process" ?

Are there any differences in the likelihood of future submissions by occupations?

Do you have any info about the academic position held? I.e., is there a tendency for pre-tenure, tenured, post-docs, etc, to publish in mega-journals, and importantly, do they chose these journals for different reasons?

Having the comments in an easily parsable format (i.e. txt, csv, ...) would be better than PDF, and probably more useful if people want to do further analyses on this dataset.

The quality of the journals is a major consideration (>20% of respondents). What makes a journal, including the sample journals, a quality journal?

More comments than questions: (1) PLoS ONE accepts submission in any scientific or medical discipline, not just biomedicine.

(2) PLoS ONE has a no-questions-asked APC waiver.

I publish frequently in PLoS ONE and both are certainly important considerations when choosing a journal.