Multisig without P2WSH in Lightning The current Lightning implementations use P2WSH script format for multisig in the funding transaction. But it is also possible to use the CHECKMULTISIG opcode "natively", i.e., without P2WSH (see Mastering Bitcoin, Chapter 7). Can it be used for channel establishment? What would be the pros and cons? Was multisig used in Lightning at some point, or did Lightning go straight to P2WSH?
The main issue about using a non-segwit inputs in the funding transaction or a p2sh output as the channel anchor is the transaction malleability. 

The recovery guarantee before a channel is funded relies on the commitment transaction building on top of the funding transaction. If the funding transactions txid were to be malleated, the commitment transaction becomes invalid and the funder becomes beholden to their channel partner for recovery. 

In the case of using a p2sh output as the channel anchor, malleation of a unilateral force-close could be used to prohibit the counterparty from punishing the publication of an outdated channel state.

Therefore the funding transaction must be non-malleable and the channel anchor must be held in a script that is not malleable upon spending.