DLink forums are for support, help and information regarding D-Link OEM products.
I recommend that you check out the OpenWRT and DD-WRT forums and there sites for what they support on D-Link model router hardware. Not all routers support 3rd party FW. Most Broadcom based D-Link routers support 3rd party FW if those Mfrs develop it.
I would check out DIR-868L, DGL-5500, DIR-825, DIR-810L or DIR-615 as prospects for 3rd party FW.