It will be great if Microsoft can allow external users to access powerapps at no charge or charge per block of 1000 users per year at a fixed fee.
Medical research institutes conducting research studies will really benefit as participants who volunteer in these research can use the powerapp share data. In a lot of cases research studies are not funded so paying per participant per month is not feasbile.
This is also allow researcher build there own apps instead of hiring a developer to develop a data collection app. The researcher could then push the data from powerapps to SharePoint or Dynamics.
Microsoft will be doing a great job in helping the research sector by providing the option to setup free external users logins.