Where can I submit feature requests?

Mojang doesn't often take in community requests for feature to be added to the game. Some current things that were first implemented in mods are:

• Horses
• Commands
• Dual Wielding
• Shaders
• etc.

Are there any ways that users can submit requests that are guaranteed to reach the developers' ears?

Yes and no. From Mojang's "Where can I submit suggestions?" page:

Please be aware that we are not actively seeking change or feature requests to Minecraft.

The best place to submit suggestions for Minecraft for PC or Minecraft: Pocket Edition is at Minecraft Suggestions on Reddit. The developers visit sometimes and view highly-rated suggestions. Because the developers can receive hundreds of suggestions a day via Reddit, Twitter and email, they will not be able to view or answer each suggestion.

The development of the console editions of Minecraft generally follow the PC version's development. If you'd like to submit a suggestion, visit your console's corresponding sub-section on the Minecraft Forums.

Feedback on the Windows 10 Edition can be made here.

If you have an idea for Minecraft for PC, you may instead want to request that a mod developer makes it into a game mod by visiting the mod request section of the Minecraft Forums.