It’s worth noting that Substrate’s account abstraction is a useful lever here.
For the Moonbeam case specifically, I’d imagine that this is the exact use-case of smart contracts. A smart contract controls an account on the Moonbeam chain, and this smart contract can handle a collaborative decision deposit.
I’m not sure about the complexity of pooling decision deposits in the pallet itself, but it’d probably be better as a separate pallet as opposed to integrated into the main OpenGov pallet itself.