RPi4 doesn't have a stable release yet, only a snapshot.
Change the lan IP/mask/gateway/dns to something that is valid on your network with vi or scp.
Connect by SSH, do a opkg update; opkg install luci
Then, I guess, I must have forgotten it. 
There is a chance that I still have the image, I'll check it out then.
Does anybody know if raspberry pi 4 1GB is supported? I see the hw page is only mentioning the 4GB version.
As far as I understand, the difference is only in the amount of memory. Just note that there is the first release and then there is rev 1.2.
The HW page does not specify rev, so my guess is that only 1.2 is supported...
The ToH shows both, though it mentions only snapshot for B, so it could be that the development stopped at that for the offer version. Anyway, the good thing about these devices is that you can't break them. You can always try an image and see if it works or not.
Anyone knows how's the stability of openwrt on raspberry?
I'm torn between this an a J1900 x86 NUC.
Mine runs flawlessly since beginning of March.
And before that?
I was using the RouterStation Pro. 
just as an aside here, I've found that the most performant way of setting this is to have the native ethernet port do Access-Point/LAN duty, and the usb to ethernet adapter for the WAN side. Thereafter, use SQM for the WAN link to configure proper queueing. LAN side benefits from MQ fq_codel qdisc setup on the eth0, and the pitfalls/limitations of the adapter are mitigated by leveraging CAKE and SQM-scripts for proper queue management rather than relying on falling back to BQL.Haven't seen this noted explicitly anywhere , so felt it might help others. Took me an inordinate amount of testing to properly establish these things. This was more to properly establish the fine-grain performance and optimize, actual throughput at maximum levels is fine mostly irrespective of this. I'd also suggest disabling all network offloading with ethtool on eth0 and eth1 if you've a connection below 100mbit, adds additional complexity that potentially adds latency to no real benefit.
To my knowledge there is only a Pi 4B version. Please note the B does not indicate that it's an improvement over A. Rather, it is different form factor. Starting with Pi 1A+, the A devices are smaller and have reduced functionality. Most significantly for this forum is that the A devices do not feature an Ethernet port.
My VPN gateway running on a Pi 4 shows
root@Gateway:~# uptime
18:25:38 up 107 days, 19:08, load average: 0.00, 0.00, 0.00
So seems last time I rebooted it was 6th of January.
Yes, that's correct.
Though, for Raspberry Pi 4 B, there is the initial revision (well, if the first release can technically be called a revision if it wasn't supposed to be revised), and a rev 1.2, which was later introduced, to fix an issue with the Pi being not working with some USB cables [power supplies], if I remember well.
[More about that here https://www.cnx-software.com/2020/02/24/raspberry-pi-4-rev-1-2-fixes-usb-c-power-issues-improves-sd-card-resilience/]
That's right, it was the USB-C port (no data, only powering) did not work properly with USB-c cables that are fitted with a chip implementing USB C power delivery 2.0. That fix is completely transparent to software and does not influence OpenWRT.
Mine runs flawlessly since beginning of February.
I wasn't sure , particularly that the ToH seems to mention snapshot for RPI 4B and 19.07.2 release for rev 1.2.
Maybe you could look into fixing that if you own one.
This rev1.2 in the ToH is in fact Pi 2 placed at the bottom.
I think I need a rev 1.2 of my glasses!
Can anybody here help me out. I'm planning to buy a Pi 4 and use my old TP Link C7 as a AP. I just had a question. Would I need 2 USB 3.0 adapters, one for a switch and the other for WiFi?