Ask and you shall receive (apparently) - ASUS has just published the bootloader unlock utility for the Transformer Pad 300. You can download it here.
Unlock Device App: Unlock boot loader.
1. Only suitable for Andriod4.0 Ice Cream Sandwich OS version.
2. Before you download, install, and use the Unlock Device App you acknowledge and assume complete risk to the quality and performance of this App, including but not limited to the following: once you activate the App you will not be able to recover your ASUS product (“Original Product”) back to original locked conditions;the Original Product with the activated App will not be deemed the Original Product; the Revised Product will no longer be covered under the warranty of the Original Product; the software of Revised Product will no longer be deemed the software of the Original Product and can no longer receive ASUS software updates; your purchased digital content may also be affected.
Considering ASUS unlocked the Transformer Prime (TF201), and that the Transformer Pad 300 is basically a downmarket variant of it (same internal hardware), this makes sense. Let's hope ASUS does the same for the Transformer Pad Infinity.