This is not an Armory thing, this is a Bitcoin-network-thing. The 0.0001 fee is actually a "relay-only" fee, which doesnt' guarantee it will be mined, only that the network will see it. Right now, that's usually sufficient to get it mined, but my goal is to minimize issues, and using the 0.0001 minimum fee is likely to result in tx occasionally getting stuck (maybe not right now, but possibly in the future).
Bitcoin-qt 8.x uses 0.0001 minimum fee per KB, so there shoud be this option in Armory as well. And if the fee ruling in Bitcoin-qt changes, you may change it in future Armory versions as well