I am trying to develop a simple alternative to GeckoOS that could be launched from HBC that has full hardware access (AHBPROT). It works so far for me when running it for Wii, but have not tested it for WiiMode in WiiU. Currently it only has the ability to launch channel and rebooter (for patching system menu, e.g. being able to move disc channel, and to copy protected save game files, like animal crossing or mario kart, to SD card).
If you have installed HBC with full hardware access in your WiiU, you could try it and let me know whether it works for you or not. Here is the link:
WiiBooter
And in case you want to help debugging it, you could get/download WifiGeckoReader (PC application) from wiiflow googlecode page or
here (compiled by me), and add the following lines into the meta.xml file in the WiiBooter folder (before the </app> line at the bottom):
<arguments>
<arg>-aXXX.XXX.XXX.XXX</arg>
<arg>-p4405</arg>
</arguments>
where XXX.XXX.XXX.XXX is your PC IP address where you run WifiGeckoReader.