I think the number of posts over the last 10+ years has always fluctuated with the "challenge" that was trying to be solved. First it was DVD playback, then perfecting DVD playback picture quality. Then NTSC TV tuner cards became ubiquitous and building your own DVR became feasible. WMC XP edition rode in a new wave of HTPC excitement, and then ATSC tuner cards exploded thead counts here. With Vista and Win7 there was a huge leap forward in ability, but no shortage of codec-problems and everyone trying to tweak their experience. When cable-card came out, we saw a renaissance in HTPC usage as DVR rather than just video playback devices. Streaming video has always had a huge demand, but the tools were either kludgy, stopped working, or abandoned. Blu-Ray (and subsequently 3D) created a lasting but minor stir here, and it seems the population has always been gravitating towards using servers, NAS, or advanced setups.
With WMC stagnant, and the alternatives are just ok, depending on your level of tradeoffs or what you are willing to put up with. I think the community has settled into a calm, enjoying over a decade's-worth of "crowdsourced" community intelligence. Microsoft has effectively abandoned the home market... both media and server. Minor players seem to pop up and make a bit of noise every now and then... streamer-boxes (Boxee, Popcorn, Patriot, Roku, etc.), alternative interfaces (Sage, Media Portal, XBMC, etc.)... but it all seems to come back to WMC. It was always the 900 lb. gorilla in the space, and I think they won a lot of "Microsoft-fans" at a critical point in time when they were seeing their most intense competition from FOSS (Linux) and Apple.
I don't know if there are any new hardware challenges in the HTPC space to be overcome. I don't think 4K video will be that much of an improvement that it will need anything more than slightly beefier hardware. Now, in the software space, there is a lot of opportunity, but no one seems to get it. Boxee had the most potential marrying the physical (locally stored video, TV watching) and the virtual (streaming services)... but really lost their way with the whole boxee-box thing. The attraction was always about their software, the strategy of making your own hardware was just silly in my opinion. Google made a little noise with their search services on top of existing services, but they were a little short-sighted in my opinion... once again... it's the software that makes Google great, not another box. Apple? Who knows... the whole "cracked the code of TV" comment by Steve Jobs has yet to be revealed. So TV for Apple is still a "hobby".
And here we are... still a "hobby" for most of us.