Reading through this thread, there are certainly other feature requests (specifically for the Roku) I'd be more interested in (e.g. Quicker Live TV grid, surround sound capability, ability to channel up/down/prev w/o having to go back to the guide), but if this wouldn't require much effort, perhaps it could be rolled out in the next Roku app update.
Assuming you're not currently changing how thumbnails are produced for each recording, I'm wondering if you could add some type of icon, symbol, or text for each recording in the Roku app that would let the user know when the thumbnail generation was complete. Not sure about everyone else, but I definitely prefer to watch recordings with the thumbnails present, so I would certainly wait the extra minutes for them to generate. But as it stands right now, I either have to wait a day (to be certain) or start watching and hope they're there. Not a big deal, but thought it would be a quick, cool feature to incorporate.
Also, and this one's more of a true road map request, I hear Channel Master is working on a service called LinearTV that will allow their DVR+ to stream internet channels (of linear TV content) and have those channels appear in their channel guide with show listings. As of right now, it sounds like it will only work with free internet streams, but I'd have to think a deal to incorporate subscription based streams (e.g. Sling TV) would be a breakthrough. I think it'd be pretty sweet to have your OTA and subscription based channels in one spot and on one guide. Probably not plausible, but who knows.