How very thoughtful of them! Asus just today published the bootloader unlock tool for the new Transformer Pad 300. Here's a quote with some details and instructions, followed by a source link to download it.
For all of our devs and tinkerers out there... you are welcome!Version V7
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.
Thanks to all of our tipsters for sending this in or posting about it previously in the forums!
Source: TransformerForums via Asus