The Xbox 360s are dead end - any replacement for WMC will require replacing them - and we have 6 of them we are using as extenders.
We have 3 potential replacements for WMC for this year - Comcast's X1, TiVo and SD's DVR.
Comcast would be rental of the DVR and satellite STBs, but that would eliminate the need to rent cablecards - which are now costing us $200 per year for the 2 cablecards in our WMC. While their new X1 DVR is a significant improvement over their previous DVR - and does integrate their streaming and VOD into the same interface - there are limitations (commercial skipping, inability to play our personal videos, ...) - plus the monthly cost will be significantly higher in the long run.
If TiVo produces a 6 tuner variant of the Bolt - we'd be able to get down to 1 cablecard (a $100 savings per year). We'd replace the Xboxes with Minis (one time $150 each) and have to pay TiVo their subscription fee - at $150 per year. The Bolt integrates the major streaming services plus supports Comcast's VOD - and also provides access to our personal media library. And the TiVo software now has commercial skipping (for the major networks prime time programs) and the 1.x playback with audio that we often use for sports programs. It would cost more than our current WMC - but it would also give us more functionality - and even better, a company actively supporting the products and program guide. The possible negatives of this option - if they don't produce a 6 tuner Bolt, then we'd have to get 2 Bolts - which would increase our annual costs by $250 - plus there is a risk their acquisition by Rovi could destroy TiVo.
SD's DVR had potential - but the functionality is falling short of what is available with X1 or Bolt. The lack of a program guide grid (while some are growing to like the slices) is probably a deal killer for family, and they've made several other design decisions (at least for this first release) that may make it less attractive (such as requiring access to their cloud servers - which seems to slow down performance of the program guide and recording features). You should be able to get the equivalent of an Xbox 360 extender for $100 to $150, and may have multiple options (unlike X1 or Bolt). Since it's taken them over a year - and they still don't have DRM support, coupled with some of their design decisions - it doesn't appear their DVR will be a serious competitor to X1, Bolt or WMC this year. Perhaps if they can get a partner to integrate the DRM support into other existing, fuller featured DVR software packages - we'd find something that could serve as a WMC replacement. But that also doesn't appear to be on the horizon for this year.
As long as we can keep WMC working, there's no great urgency to find a replacement for WMC. WMC continues to work very well for us - and if we do shift, because of the investment required for new hardware, we'll only do that if we have confidence it's a solution we can use for at least 5 years (to justify the short term costs).