There were a couple things that I pondered on a bit during the course of the research, but that weren't necessarily within the scope of the paper (which was written for a diverse audience that might not be terribly interested in the more technical details of the work).
1. The first obstacle I ran into in my own work was how to organize the e-mails. The interviewee would tend to type a few short responses to a question, but they would be in separate e-mails throughout the day as he remembered more about an event. I wanted to organize them by subject, but worried this classification would have caused these e-mails to become separated. Right now, they are organized by date, where I can look at the string of responses, although that makes it hard to find specific pieces of information. Eventually, I would like to take the e-mails and copy them into more of a 'transcript' format, which can then be a text-searchable document, but I haven't gotten that far yet.
2. Privacy concerns were something else I grappled with. Obviously, there's a level of confidentiality you need to respect when working with interviewees: you don't, for example, want to reveal their real names without their express permission. One thing that really excites me about this type of interview is how easily we can share the contents of those interviews. For example, posting an interview online would be especially easy and would allow others to more easily access historical information from that person's vantage point than they otherwise might. What I wonder about is how to balance the desire to share history with the desire to protect privacy. How do we navigate the need to ask permission before sharing information with the fact that such information can be so easily copied, pasted, linked to, etc. once it's online?
3. I also feel like this format is constrained by being accessible only to interviewees with a certain level of privilege. For example, e-mail is not a practical solution for interviewing elders who might not own, or know how to use, a computer. Similarly, people living in poverty may not own computers, and it may be prohibitive to go to a public space with free internet (i.e. rural users trying to access the local public library, particularly if they have to buy gas/bus fare to make an extra trip there). However, I've discovered it's a great way to conduct an interview with someone who is hearing impaired but still has decent vision. It's also great for people who don't have much time to devote to the interview process. I guess with any format there will be those who it privileges more than others, but it's still a useful thought exercise.