One can only speculate as there are only two other single-letter .com's (q.com and z.com) and there won't be others [1] . Wiki article says "GMO Internet, Inc. purchased Z.com for nearly $6.8 million from Nissan, who previously used it for the Nissan Z series cars." [2] For comparison, asking price for b.org or r.org are $500k but .org's typically command less than .com's.
It has to be worth a lot less than that today. The number of young people who visit websites ever in any given week is dropping. Reddit's usage among young people shot up after mobile apps were developed for it, not before. Domains just don't matter as much anymore.