Are there any plans for updating Electrum plugin and making it easier to use for newbies
There is a plan for that but there is no roadmap or ETA.
maybe adding app for hardware wallets like Ledger or Trezor?
That would be amazing, even if not supported fully by manufacturers of hardware wallet devices.
Hardware wallets use seeds to generate private keys. You cannot import private key into hardware wallet - it is impossible to use them to keep ChipMixer chips private keys.