I wonder if offering permissively licensed HDL implementations would help uptake on the hardware side.

I started a Verilog implementation of part of Daala with this kind of idea. Google also provides a VP9 HDL implementation which has been included by a couple of chip vendors.

However, such a fixed purpose decoder is going to have to compete in die area with other video decoders on the chip. I feel that a better solution is DSP-based video decoding - examples include Broadcom's VideoCore. This is actually how most video decoders already work, but you generally can't edit the code. These decoders give the speed and low power of a dedicated hardware decoder due to special-purpose function blocks, but are still flexible enough to decode different video formats and include bugfixes after the hardware has shipped.