I haven't but apparently it routes a full GigE no problem, and handles 100Mbps OpenVPN without any encryption hardware.
I've actually got an espressobin as my fallback hot-spare router, and it definitely is able to use my custom HFSC based shaper at 400 Mbps, maybe more. The Pi should be faster.
None of the issues that @diizzy linked to are relevant to routing load. It is true that the device is relatively new so there may be some quirks that get ironed out in the next bugfix version, but I don't think any of it is showstopper for routing, particularly considering that people are saying things work well for them so far. I have yet to see anyone post here "Hey I installed OpenWrt on my RPI 4 and I'm having problem xyz" whereas I have seen several people say "hey it works and is fast!"
When the quirks get ironed out in the RPI 4b or whatever, buy one for $35 and swap it in 
If after 1.5 years of continuous usage it borks, buy another one for $35. One of the huge advantages of the PI is it's available all over the place. Get a high quality power supply though!
Most of the problems posted here on the forum are associated with trying to get the PI to handle wifi as well... don't do that. Inevitably the antenna is important, and the Pi basically doesn't have what it takes even if there weren't problems with the drivers etc. just disable the wifi on the Pi. It's a lot more powerful than an Edgerouter X at a lower price.
I held off for a while recommending the PI mainly because it had ethernet hanging off a USB 2 interface! but I'm doing it now based on my experience with Espressobin and knowing that the PI4 is more powerful than the espressobin, and there are several reports of satisfied PI4 users here on the forum... But it's not a slam dunk. On the other hand, neither is the R7800 a slam dunk, people had a bunch of latency related issues for example: Packet loss and Latency R7800
And on the Zyxel Z2 (same hardware) weren't there reports of jumbo-frames causing the whole kernel to bork?
Right now it looks like the RPI4 is a solid option. If you want to go more than 500Mbps you should add a USB 3 gigE dongle... or better yet start thinking about an x86. Though I think you can route the GigE with a USB3 ethernet device if you don't care about SQM. I'm just guessing with SQM it'll top out around 500Mbps based on my espressobin experience, but it might go 600 or so... I don't know.
500Mbps is about 42000 packets per second for full size packets. That's 36k cycles per packet at 1.5Ghz.
Perhaps if you bonded a USB 3 dongle and the built-in ethernet, and used a LAG group on the switch you could employ two cores? It's all theory until someone tries it out.