After doing a lot of reading here, I decided to take the plunge and upgraded to the 3.0.0.4.384_9165 firmware. I ended up running into a lot of issues, and thought I would share here.
I use dual WAN link aggregation on my AX-11000 router connected to my Netgear CM1100 Modem. This enables me to get slightly over 1.25GB download speeds with my Xfinity 1GB service. (uploads still cap around 38MBs, but that is different story). When I upgraded, I could not get the dual links to work. The Router kept starting the wan port, then flashing RED on the front for WAN and then shutting down. I had done a complete NVRAM reset (hold WPS, and power on), but still no luck. I did this several times to be sure, and rebuilt my configs from scratch. NO luck. I double checked the cable modem to make sure link aggregation was enabled. I ran through the logs on the ASUS and there were crashes and errors all over the place, but nothing that I could specifically pinpoint as the root cause. I was not at this point changing any settings sans the dual wan. I could not get it to work.
That was strike 1. I could live with the link aggregation being down for a while as most of the time I'm on wifi, and only rarely on the 10GB NIC to achieve <1Gb anyway.
Strike 2 is the mesh. I use a pair of ZEN XT-8's for my mesh routers, both connected on the wan port at 2.5Gb. ( I have a netgear MS510TXPP downwind of the 2.5GB port on the AX1100). Both were working fine at version 8011. On 9165, I could not get both to come on line simultaneously using the ethernet port. During the upgrade I had moved those to firmware _25224. I did the NVRAM reset on them as well, and could find them and pair them on the 5ghz wifi. When I switch the default link from auto to Ethernet on the first zen, it made the change. On the second one, it would just completely drop offline if I did the same thing on dropdown GUI. Once it dropped off the only way to recover it was to reset and re-pair the mesh. I thought I had one bad unit, so I reset both, swapped the order of pairing, and sure enough same thing - only the first would stay linked on Ethernet. Adding the second unit works on Wifi but crashes completely trying to switch to Ethernet I ran through the logs and there were a lot of system crashes, reboots, and general mess.
Strike 3 was VPN. I use open VPN for linking some routers at parents and in-laws to keep an eye on things, and help with troubleshooting, as well as a link for my laptop to route all traffic when traveling to avoid insecure hotels & airports etc. VPN simply did not work (as most people have said here). Nothing in any config, log or error made any sense.
After several hours of tweaking and playing and adjusting settings, I said the heck with it all and went back on the ax1100 to _8011 and magically everything worked (zen xt8's back on ethernet, dual wan and all my VPN connections.
So for now, unless someone else has a solution, _9165 is a mess and should be avoided if you use any of the above services.