Alternatively, I think the research could be done in an isolated experiment environment among consented participants. For example, they could ask maintainers to

Alternatively, I think the research could be done in an isolated experiment environment among consented participants. For example, they could ask maintainers to review some set of patches outside the context of Linux kernel. They would then ask maintainers opinions on the said patches using some form of questionnaires. If the participants are well informed the nature of the experiments, there would not be any ethic concerns. For incentive, the researchers could pay for any maintainers willing to participate the experiments.