Only Roku could add a DVR ability in and I doubt they would do that as some of the companies providing free channels may not want them to do that. Besides 99% of the stuff out there is streaming on demand so a DVR is not needed. Sling TV is the only reason that I can think of where you want a DVR (other than Tablo) but that's up to Sling to provide a solution. Their main solution was to have most of the channels auto record up to 3 days back but not everything works that way.
Now for ESPN, keep in mind you don't really need a DVR for that. If you install the Watch ESPN channel you can view previous sporting events on demand with ought the need of a DVR. This is part of your Sling TV package.
Roku would never add a DVR feature to their boxes for streaming content or their channel count drops quickly.
Watch ESPN is great, I love it and finally have access to it with DirecTV, but DVR features aren’t available. I’d like to be able to rewind and fast forward when using it, but can’t.
Anyway, adding apps like Watch ESPN and then offering DVR features wouldn’t be up to Tablo at all, that would be 100% up to the channel owner to decide to implement if Tablo ever went the app route. To me, one of the most intriguing things about Tablo is that they chose to fit in with the devices that people already have and use instead of bolting Netflix and Hulu+ onto their interface.
MythTV also does what that Kodi link above does. Nothing really new there. Lots of options if you are willing to tinker and maintain yourself.
I’ve given up on that and gone the appliance route fully knowing there will be limitations.
I guess I took the opposite direction. I had a PalDVR for several years and it was awesome with a great guide, but last year they quit providing a TV guide. It finally died a couple of months ago, so I did a lot of research to find a replacement. I wanted a free or inexpensive guide, 14 days of guide data and above all inexpensive.
I looked at the Tivo, and an excellent device, but wayyyyyyyy out of my price range. I looked at the other boxes like the channel master boxes, but they had problems. I was ready to purchase the Tablo but it was also a little expensive, but I am sure it is a very nice device. Since I already had several Android boxes that were using my PVR backend running on my older Synology NAS, I figured I would try to make one of my Android boxes into a PVR, at no cost at all to me since I already had all the hardware. None of the Android boxes made before the last six months, had the power or capability to work as a front end for the HD channels coded in mpeg2 TS streams, much less as a server.
After loading OpenELEC onto my quad core Amlogic box, and installing tvheadend server, it greatly exceeded my expectations as a stand alone DVR, but also a DVR server for my other Android boxes running Kodi. In other words, with this one box running a PVR backend, all my other boxes have the same capability and functionality of a DVR.
Kodi and OpenELEC have come a long way, and now it is just install it and forget it.