they're not going to give anyone the code for the kernel, the SDK and Brightscript components for firmware 4.x has not been made publicly available yet and there has been no time line offered on when it will be.
If you don't understand open source licensing, this might help. In short, Roku chose(wisely, imo) to build their product, in part, upon other people's code; and therefore to agree to the terms of the license(s) that code is under. Part of that agreement(depending on the specific code/license) is providing access to those parts of product's code (and any changes made to to them).
OP, I suggest sending a private message to RokuShawnS (the forum liaison). He should be able to facilitate your request.
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my apologies. I understand open-source GPL just didn't realize the Roku was built with it because of talk I have heard about the kernel being locked down. Possibly a better contact for the OP would be one of the developer forum guys like RokuPatrick, etc.