Has anyone had any success in finding a server on Electrum, Sparrow, or another popular wallet that supports broadcasting of transactions that pay below 1 sat/vByte? Besides Blue Wallet, have other software clients signaled that they will make changes in this regard?

I don't think manually editing raw transactions and exporting and importing from Electrum to Bitcoin Core is something many people would be interested in doing. It seems that's the only option for now.