A forward with size who seems to be transitioning well to the pro game, who's still very young, will have value. I can't see how Harris could have similar value, and Barron.... would be reasonably close if he were having a good transitional season, but he clearly still needs work on his defensive game, so he doesn't have that kind of value right now. Maybe we revisit in 15 months, when Knies' ELC contract is up and perhaps Barron has taken a huge step forward.
Savard ? Comparing kids to rentals/quasi-rentals isn't going to be productive, since the vets fetch crazy prices when they fit the perceived need. That being said, I don't see why Toronto would sell off a kid currently in the lineup if they are trying to improve said lineup, and their window is still pretty open, and will stay open once Tavares gives them serious cap room to work with.
Like I said earlier, for Toronto to move him, it would have to mean getting a player entering his prime who would be around for that whole window. Ignoring the cap for a second, perhaps a Josh Anderson-clone who was actually scoring goals and had been playing well for the past 3 years would have that kind of value (ie, trading potential for present performance), but sadly, he hasn't performed (not even close, if we're honest), so he doesn't hold that value.