Is there a way to "follow" a question (i.e. get a message in your Stack Exchange inbox whenever someone comments on or answers it)? If not, can that feature be added?
Such a feature does not currently exist.
Below is an alternative that gives you some of the functionality you want, using third-party tools. (I wrote it initially based on an incorrect assumption that you meant "email inbox" and present it now as a side point.)
Using RSS, you can subscribe to answers and (I think) edits to a question, but not comments. On the bottom-right of every question feed, there's an RSS link labeled "question feed." If you use an RSS reader such as Google Reader, you can put that link into it to get updates there. You can also sign up for an "RSS to Email" service that will make the RSS feed into emails for you.