From the description of TVE, the required hardware includes:
c. Linux PC or NAS using a 64-bit Intel CPU
I'd guess this is to support hardware decode/encode, which is something being actively pursued with the Pi4. So stay tuned. You could allocate another PC to this task for a couple months and revisit. For standard MPEG2 stream DVR functions, as well as limited live transcoding, it's already working great for me.
The Pi should work for TVE if you run:
sudo apt-get install chromium
I tried that and successfully installed chromium however when I try and add my TVE login for DirecTV and Philo but still get Context Cancelled... The hdhomerun portion works great though!
2019/08/19 10:41:43 [TVE] Auth starting for DTV as [email protected]
2019/08/19 10:41:43 [TVE] action=auth mvpd=DTV requestor=nbcentertainment
2019/08/19 10:41:46 [TVE] action=navigate url=https://sp.auth.adobe.com/adobe-services/authenticate/saml?noflash=true&mso_id=DTV&requestor_id=nbcentertainment&no_iframe=true&domain_name=adobe.com&redirect_url=https%3A%2F%2Fsp.auth.adobe.com%2Fadobe-services%2FcompletePassiveAuthentication
2019/08/19 10:41:46 [TVE] action=request type=Document method=GET url=https://sp.auth.adobe.com/adobe-services/authenticate/saml
2019/08/19 10:41:46 [TVE] Auth failed for DTV: context canceled
2019/08/19 10:42:38 [TVE] Auth starting for Philo as [email protected]
2019/08/19 10:42:38 [TVE] action=auth mvpd=Philo requestor=AMC
2019/08/19 10:42:39 [TVE] action=navigate url=https://sp.auth.adobe.com/adobe-services/authenticate/saml?noflash=true&mso_id=Philo&requestor_id=AMC&no_iframe=true&domain_name=adobe.com&redirect_url=https%3A%2F%2Fsp.auth.adobe.com%2Fadobe-services%2FcompletePassiveAuthentication
2019/08/19 10:42:39 [TVE] action=request type=Document method=GET url=https://sp.auth.adobe.com/adobe-services/authenticate/saml
2019/08/19 10:42:39 [TVE] action=request type=Document method=GET url=https://idp.philo.com/idp/sso
2019/08/19 10:42:39 [TVE] action=auth_domain domain=idp.philo.com
2019/08/19 10:42:40 [TVE] Auth failed for Philo: context canceled
Should I return my rpi4 and look for an intel nuc instead? I was trying to keep the server as budget as possible but I'm sure I can find an older NUC on ebay.
If you don't need remote streaming/transcoding, then the Pi4 will be fine. Aman mentioned that as long as you have a chromium package installed, then TVE ought to work.
Update on PI 4 progress: our developers have managed to implement both scaling and h264 encoding in hardware on the PI4, and it's working very well, and is quite stable. I only have 5mpbs uplink speed, but can now stream using a 720p4mpbs setting outside my LAN, both in the app and in the web interface. I doubt I'll use it much, but it's great to have. Most impressive is the CPU load during all this stays below ~150%, sometimes below 100%. That means you don't need to overclock, and maybe don't even need a fan, and can use the Pi for plenty of other things at the same time. A heatsink and vertical mounting may be enough cooling. Anyway, there is more testing to do, but if you have a Pi4 on hand already, I strongly recommend giving it a try. The $35 1GB model should suffice.
FYI, I have TVE running nicely on my Pi4 with recent betas. Just had to sudo apt-get install chromium.
When I run that command, it gives me the following error:
"Package chromium is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
However the following packages replace it:
chromium-bsu"
I just ran the same command and replaced chromium with chromium-bsu, and it seemed to work. Do you know what this means?
EDIT: Apparently I just installed a video game 
EDIT2: It finally worked, but only after I updated my Raspbian OS with the following commands:
sudo apt update
sudo apt upgrade
Sorry for the messy post with multiple edits, but hopefully this will help others.
I just installed Channels DVR Server on Raspian on the Pi4 and I have everything working with OTA and Philo. I am trying to add YouTube TV next and when I attempt to add it as as a TVE provider, it attempts to login and says "context canceled". I have verified that Chromium is installed, the OS is up to date and patched, but still no joy... I have also logged into YouTube TV through Chrome on the Pi and NBC Live (authorized live playback) and both work through the browser. However, it made no difference when trying add YTTV as a TVE provider - all the same result, "context canceled". Any ideas what to try next???
Update to the latest build of the DVR which has a fix. Click and hold on the "Check For Update" button.
ahhhh!!! That was the trick hold the check for update button! Thanks!!!!
I just installed Channels DVR Server from (https://getchannels.com/dvr-server/#rpi4) on a Pi4 with a fresh install of Raspian. I ran the script on the locally mounted HDD (WD easystore 4TB). I get an error when I try to use the web interface for configuration. and my Shield TV can't see the server.
What error?
This site can't be reached
I think I got it, I had to double click the "Channels DVR" executable file in the "Latest" file and it started working
That is not recommended, as it will lose your settings on reboot.
Please check what the channels-dvr.log file says
I've gotten Channels DVR on Pi4 and live tv streaming works through TVE (after Chromium on Pi). However, I can't get the DVR recordings to play on my Apple TV through the Channels app. Any tips?
What exactly happens when you try to play?
I don't see a .log file
It should be in the directory where you installed the dvr, under data
What does this command show:
systemctl status channels-dvr
Or this to try starting:
systemctl start channels-dvr