I contacted support the other day with a similar question (whether they have plans to upgrade sandbox) and I still haven't had an answer one way or the other. I'd be surprised to see Sandbox upgraded before it gets bundled on wordpress.org, and I can't even remember what the timeline is on that.
Staff will probably tell you that they'll consider your request, but I wouldn't take that too seriously. As well as the risk Mark mentioned of breaking stuff and upsetting people, there are a number of other obstacles: themes need to be heavily edited to work on wordpress.com (and a lot of that work might need to be re-done), there are too many themes to make it feasible to keep track of new versions (if we only had a dozen it would be manageable), and the majority of users would rather they spend their time adding shiny new themes than upgrading boring old ones.
So theme updates are very low on the priority list. If you really want to run the most current version of a theme, you'll have to install wordpress .org and download it yourself.