He suggests that the format should be either an already valid PSBT or one that can easily be converted into such. His proposition includes a standardized descriptor file that could be loaded by a coordinating device to simplify the process.

Brandon outlines potential additions to BIP174, which is the Bitcoin Improvement Proposal related to PSBTs. These additions would include two new global types: PSBT_GLOBAL_DESCRIPTOR and PSBT_GLOBAL_KEY_NAME. The former would have a key represented by "|" and its value would contain the descriptor encoded as proposed. The latter would consist of a key "<keyname>" and its corresponding value. This structure aims to facilitate communication with compatible signing devices by standardizing how descriptors and key names are incorporated into the PSBT without necessitating further modifications.

By incorporating these changes into the PSBT protocol, Brandon envisions a more streamlined interaction between coordinating devices and signing devices, wherein the former can add inputs using PSBT version 2 or an unsigned transaction using PSBT version 1, and then seamlessly send this information to the latter for signature verification and completion of the transaction process.