If you have many users who each only need say 4MB/s, then hard drives would struggle whereas SSDs would not. Gigabit Ethernet would also still be sufficient even without using ganging, so 10GbE would be unnecessarily expensive and would require the clients to also support 10GbE, which isn't likely in the home. The product has its uses as it is, though I can't help but feel that two 2.5" slots would have been better since you could then choose to use HDDs or SSDs, depending on which better suits your needs.
Something like making the Ethernet ports be through a replaceable module that could be switched out with a 10GbE version would be a nice touch too, but I doubt many people would do something like that and it might be easier to just later make a 10GbE version of the NAS for such customers.