The paper suggests a soft-cap to combat "Forced Expiration Spam".
An attacker who causes many of the channels to be prematurely closed at once could overwhelm the network.
What happens in the opposite case: if an attacker tries to fill the channels with unsettled / open transactions, by breaking, say, 100 bitcoins into billions of transactions of few satoshis and letting them intentionally unsettled, so to speak, for the lolz...
I'm thinking whether the LN network can be bloated to such an extent that it becomes unusable, if the proper fee or dust disincentives aren't placed there (?). In general there are very few scenarios where very low cost use can't lead to very low cost abuse.