Flash chip is on the back and looks like WSOIC-8 SPI flash (could be SPI-NOR or SPI-NAND). Luckily they used that (and not the parallel NAND which has traces but isn't unpopulated...), so we have all options even to replace the entire bootchain quite easily.
2.4 GHz WiFi looks like directly connected to MT7622BV SoC, so it's the MT7615-like 4T4R WiFi 5 built-into MT7622 just like on Linksys E8450/Belkin RT3200 and Xiaomi Redmi AX6S.
The combination of MT7915AN+MT7975AN is for 5 GHz.
So yes, also using MT7531 switch makes it very similar to other existing MT7622 devices, hence it should be possible to port ARM Trusted Firmware, U-Boot and OpenWrt/Linux only by inspection of a complete bootlog captured from the serial console.
i will try to get a full serial bootlog once i get home later today. i also will look into it more and post my own pics of the internals as when i was in it yesterday it looked like i had a diferent rev board.
all the internals on my unit match the fcc pictures, the shields are differant and i have not had a change to look at the back.
Probably the partition layout is slightly different from the RG-EW3200GX PRO board. Dumping the environment of the stock bootloader should tell you about the relevant parts, ie. where U-Boot wants to load the uImage containing OpenWrt kernel.
So to try you can modify the partition layout in mt7622-ruijie-rg-ew3200gx-pro.dts and try matching the start of the firmware partition with the what U-Boot tries to load the kernel from.