Instead of only providing a solution, please allow me to guide your mind along the path that leads to the solution, so that as many people can benefit from this as possible. So, you want to be able to do incremental backups to non-local storage, and you asked:
Is there any way to fix this? If not, is there any outlook on updates that fix this?
So the answer to these questions is no, but only because there is nothing that is technically broken that needs fixing. Based on the restrictions of the Windows Server Backup software, it is most likely that incremental backups are implemented through the use of SCSI commands, which means that network attached storage (NAS) is not technically a viable backup destination. But remember for a second that an external storage array connected through a native SCSI interface will work. And also remember that any storage such as IDE disks or a storage area network (SAN) connected through ATA, SATA, USB, Firewire, or a number of other interfaces are all supported. So how does that work if the software is using SCSI commands? All versions of Windows in the NT lineup (including Windows 2008) make use of a software driver-based SCSI bridge to communicate with non-SCSI devices as though they were SCSI devices.
...which brings me to your last question:
If not, are there any other methods I could / should use?
So you'll be relieved to know that the answer to this question is yes. Based on my introductory paragraph, I'm hoping that you will have asked yourself "okay, so is there perhaps some kind of driver that I can use to send SCSI commands over the network that will make it look to the operating system like a local disk?" And in asking that question lies the solution, and its name is...
iSCSI does exactly what you need, and the Microsoft iSCSI Software Initiator (client) has been built into all versions of Windows since Vista, and is available for free download for all versions of Windows since XP. Microsoft's iSCSI Software Target (server) is only available for Windows Storage Server as far as I know, but for your scenario, you could always keep things simple (and free) by using the free version of the StarWind iSCSI target for the basic purpose that you have.
While not the most ideal situation from a performance standpoint over long distances, iSCSI opens up all sorts of possibilities for solving problems where the hardware equivalents are just completely out of reach of many smaller organizations and individuals, and also where you might want to have storage located off-site, but still be able to access it as though it were local. Either way, iSCSI is not going to perform much (if at all) worse than a NAS-based "copy" style backup. So the application possibilities range from backup solutions to database clusters, and even to home use, such as extending the local storage of your DVR to a multiterabyte home server that might otherwise not be practical to have in the living room due to the noise.
Of course, if you are really just looking for a way to keep an up-to-date copy of everything on a NAS without having to copy everything every time, you could just settle for robocopy.