aggregating multisig partial signatures
I ran a M/N multi signature account locally. From what I noticed, there is no aggregation command in cli-wallet or RPC to aggregate partial signatures and the process of finalizing transactions has a sequential order.  Alice who generates the transaction needs to send it to Bob, Bob needs to sign and pass to Carol and so on, until the transaction is signed by the threshold size and ready to be submitted. Are there any commands or RPC API for Alice to be able to gather all the signatures from collaborators and aggregate them to make and submit the final transaction? In other words, I want the process to be done not in sequential order but in parallel. 
Also, I noticed that there is a maximum limit(16) on signer numbers participating in the multisig account. You have mentioned that in order to be able to support more signers efficiently, the key exchange phase should be done FROST style. Is there an implementation of this? how can I remove the limit of signers?