These are pretty good ideas! :3 Here's my opinion~
Tail length -
Oye, yes, that would be a good feature! But, could you describe it more, say, you mean custom-length, like the custom height, or just a few different options, like short tail, medium tail, or long tail? Overall it it, yes, a nice idea, but it would take a lot of coding and time for Kovu to do. ^^
Marking Coloring -
Yes, this is a very common idea, and a lot of people like it. :3 But it's a bit much, and as said above, a real pain to code. I like the idea ^^
Marking ideas -
Very good idea, and well said, but the markings can easily be made on your own, as a custom. You can also download other's custom markings, that are free, of course. ^^
Collar option? -
There already is a collar option, but it is only for the lions, which one, I rally don't understand, and two, I don't like. Because well, collars are for dogs, and two, I prefer wolves & dogs. I think it should be available for both. ^^
Ideas that I cant name -
All I can say is - EXTREME lag! there's no way I'd be able to stand FH, because it would be only lag.
--100th post, wooot~-