Theres loads of HD414s about, no need to bring that back.
Stax SR-5N/Gamma/etc type phone, except stick the 001 portable plug on it.
ESS AMT, because the prices on ebay are bonkers stupid for what it is.
Float Electrostat, except this time, done right.
Better than this talk of ressurection. Get the players in the current market to realise that their hard-ons for moving-coil drivers are a silly fetishistic pursuit and that there really is a market for isodynamic/orthodynamics out there.