Will Zcash support Multisig?
Zcash transparent transactions work just like Bitcoin transactions, but for private transactions i don’t think it is possible.
Thanks, with the correct terminology I found more info here: Home · zcash/zcash Wiki · GitHub
How would Zcash slot into existing Bitcoin businesses that are using Multisig, e.g. for escrow payments?
Those businesses would use transparent addresses for multisig.
Not for private transactions initially, but this is a possible future feature: privacy-preserving multisig transactions · Issue #782 · zcash/zcash · GitHub . The “multisig JoinSplit sandwich” approach described on that ticket can be used as a workaround for some purposes.