Game updates usually happen when the developers feel that they're playable, fun, and ready for release.
For Minecraft: Java Edition there are snapshots listed on our home page showcasing upcoming features before the final release. For Minecraft for Android devices, Xbox One and Windows, you can try beta versions.
Note: If the information hasn't already been posted publicly, we cannot give you a release date.
You can keep track of updates at Minecraft.com.
If you have suggestions for Minecraft, you read Where can I Submit Suggestions?