we have now implemented same forementioned light client desing into our penumbraprax wallet fork called Zafu that is now available for willing beta test users in chrome store altho recommended path is installing via our automated build workflow in github releases to have latest patches(google seems painfully slow.
we have also multisig fully working with airgapped cold wallet signing and we are currently working on first application that utilizes multisigs as escrowd peer to peer poker(mental shuffle, each turn signed).
we have open our grant request for conducted work over the last 8 months and hope to hear your feedback on it here.