In all honesty, I don't think this is very common nowadays. If you're migrating from something like a Nokia 1100, your contacts might be in your SIM, but most users are migrating from another smartphone in 2015, and smartphones don't store contacts in the SIM.
To be completely honest, I was unaware the modern smartphones could save contacts to SIM rather than internal contacts db(I quickly looked at my phone and failed to find an option to save-to-SIM).
This is a very very edge case that most people will never use, so lack of support for it is quite acceptable. Mainstream features are what Ubuntu is probably targeting right now.