Unfortunately, the wifi chipset will never work on OpenWRT as BCM5357 will most likely never be supported by recent kernels. So, I decided to convert my WN3000RP into a VPN Server.
I compiled 19.07.02 to have best performance with minimal footprint.
I share my ROM if anyone also want to use his WN3000RP as a small VPN Server (or Client). This ROM provides LuCI, Firewall and VPN (OpenVPN 2.4 + Wireguard).
You can overclock it to 500Mhz to have good performance. Please read instructions carefully, especially the instructions to flash and revert to another ROM, as this ROM reclaims 64kb from the POT partition. All the instructions are in the README. Sources are also included in the archive.
Use the Netgear WebUI to flash the FlashRom. Backup the POT partition and NVRAM data from the LuCI flash menu.
Then use the LuCI interface to flash the VPN ROM.
Reverting to standard firmware (or vendor firmware)
-Use NMRPFLASH to flash the FlashRom
-Use the POT-Restore ROM to restore the POT header (you must force the flash in LuCI)
-Restore the POT backup using mtd -r write /tmp/pot_backup.bin POT (where pot_backup is the file saved initially)
-You can then restore any ROM you want
You can overclock the device to 500MHz through SSH by issuing the following commands:
nvram set clkfreq=500,250,125