I've done rootbeer flavored beer using several different brands of extract.
The first time I tried it there wasn't enough sweetness left after the ferment, so in order to salvage the project I made a brown sugar syrup and dosed the finished brew with that along with some potassium sorbate to arrest further fermentation.
Second time around, in order to avoid the additive, I backed off on the hops somewhat (but not too much) and used a lot more crystal malt to ensure that there would be enough sweetness. Came out really nice, sweet but not cloyingly so, and an interesting intermingling of the hop flavors with the flavors that came from the rootbeer extract. I haven't made the stuff since I've added Honey Malt to the cupboard, but it seems to me that it would be a very good addition to this concoction.