New form of 51% attack via lightning's revocation system possible?

In this email exchange, Christian Decker and René Pickhardt discuss the potential for a 51% attack in Lightning Network. Christian argues that such an attack would be deadly to all blockchains and that Lightning participants should not be able to own more than 2 or 3 times the amount of BTC they have in payment channels. René presents an attack scenario where an attacker with 51% hash power, who already has a lot of bitcoins and well known to honest nodes in the network, can open several lightning channels and accept incoming payment channels. The attacker secretly starts mining on her own and spends fraudulent (old) commitment transactions, which she could do as the output return funds are delayed for to_self_delay blocks, giving her enough time to mine the blocks. As soon as the attacker has mined enough blocks that the commitment transactions cannot be revoked, she broadcasts her secretly mined blockchain, stealing up to 99% of all the bitcoins allocated in the sum of all payment channels the attacker was connected to. René notes that this attack is more problematic and makes it way more interesting for a dishonest fraudulent person/group than a classical double spend attack.