Legacy or FlyerChief NKP Berk with flashing Mars light
More add on's for the Polar Express(your going hog wild on the O scale side, need some more for the S scale version!)
and I agree on a fast track grade crossing with working flashers, along with more scale signals and such.
Lionel has the chance to really reinvigorate the whole AF line if they choose to. Take American Flyer where AC Gilbert might have if the company had survived and prospered the way Lionel has. Despite a high price, I am betting that legacy berks would sell. Or meet the demand half way. upgrade the details to road specific on the Flyerchief berks. NKP with flashing Mars light and correct whistle sounds ect. If they can do the mods to the Polar version, that means the tooling is modular and able to be changed around. Like NKP with Mars and C&O with lowered headlight.