There isn't any reason they couldn't do the same for HEVC or H.266 as long as the hardware support was there.
The practical problem with HEVC licensing is that it's complex and uncertain. There are three separate patent pools (MPEG LA, HEVC Advance, and Velos Media) and there are other licensors who aren't in any patent pool. The licensing situation is so bad that Leonardo Chiariglione, founder and chairman of MPEG, calls HEVC an "unusable modern standard":
http://blog.chiariglione.org/a-crisis-the-causes-and-a-solut...
A while back the x265 team pleaded with the industry to sort out the HEVC licensing problems, but that never happened:
http://x265.org/proposal-accelerate-hevc-adoption/
HEVC licensing may be too risky for the Raspberry Pi Foundation. It's simpler to use H.264 and VP9 today and to look to AV1 for the future.
Four pools — also Technicolor.