I assume they are taking the fee out of your channel balance, so it will be beneficial for you to have the fee they pay on the funding transaction be lower.
The fee is 0.1%, with a 1000 sat minimum. I paid 1000 sat, ACINQ paid more than that to open the channel.
I think in the future, it would be more common for channels to be funded via both parties sending coin in the same transaction.
More inputs means more transaction fees. I can imagine a future in which for LN users don't open their own channels at all: you just buy LN balance at an exchange, the exchange opens large channels, and you use their channels for buying coffee.
I saw estimates of exchanges holding a couple hundred billion dollars worth of crypto. Adding a few bucks for custodial coffee payments shouldn't be a problem.