Nintendo have released an update for DSi in the USA, and perhaps other regions of the world too. The update don't seem to add any features but more than likely will block flashcarts.
Nintendo DSi & Nintendo DSi XL - System Menu and Feature Updates
Most Recent Update:
December 11, 2012
Nintendo DSi Menu Ver 1.4.5U
This update provides behind-the-scenes improvements to system performance.
source - http://www.nintendo.com/consumer/sys...nuFeatures.jsp
This is the DSi, I don't see any reason to update it anymore. I think this will be the last update we see for the DSi. The updates don't add much except the feature of blocking flashcarts. It's probably safe to say that Nintendo's main focus handheld wise will be the 3DS. I would check the website of your flashcarts manufacturer for updates. The last few updates have blocked most of the flashcarts and now there are only a few that work anymore with the current firmware. If you really need to update your DSi then you may need a different flashcart unless your flashcarts hardware will still allow compatibility thru updates.
yeah, good thing DSTwo still going strong it seems, see they have it updated posted on 12/24 for the 1.4.5x update...