... Personally I don't support include this feature inside a router. I'd rather it has finer control of router and firewall functionalities as well as more stable.
A router like the DIR-655 with its limited CPU and RAM will never have the same performance as a NAS, so even if D-Link would implement this feature 99% would be unhappy with this and crying for more performance.
I can't imagine that a buildin "NAS" would perform better than Shareport.
Ethernet (Shareport) is a more versatile solution as it does not only suport one printer or one HDD but also scanners and more devices connected at te same time via USB HUB.
Of course there are limitations in this "Silex" solution but at least it works with a wide range of devices and is probably sufficient for most home networks but not for power users.
But we should all remember: we bought a router/internet gateway and not a storage solution.
I would never exchange my Synology Diskstation with a HDD connected to my DIR.