i'd love to see LAN support.
Specifically because i'd like to use Transmission to move files from one computer to the other on the same network.
I'd also like to see Multiple clients on the same LAN that are DLing the same file Sync up. If i've got it at 45% and another client on the LAN has it at 60% and another at 56% Sync all the files they have together, increasing Speed of download on the same network, and reducing the amount needed from others. Also, make it so it does not add to the global upload to encourage seeding outside the network.
You could have an extra option in the prefs panel about LAN speeds, a DL limit and UL limit and time separate from the Global. Call it LAN Upload speed and LAN Download speed.
Something i'd really like to see.
-jeremy