So the real feature request sounds as "don't lease the IP address to the host with the installed local-administrated bit in address". Sounds interesting, will reconsider this.
MAC addresses ranges are allocated just per-vendor and rather randomly. To be honest, I don't understand where one can use ranges. Do you want to block all Realtek devices, but to allow all Intel ones? Sounds strange.
1. Do you really use profits of the autoregistration in this case? Maybe it's enough just to turn it off?
2. This request can be considered in the future, thanks.
Could you please tell us what features of the fourth version do you need?
We don't upgrade because transmission 4.0 uses C++ inplace of C, and consumes significantly more CPU, RAM and flash storage.