.35 rem
The .35 Rem always had a loyal following in both the Marlin lever rifles and the Remington 14/141 pumps, as well as the semi 8/81 line. When scopes became accepted and reliable on deer rifles, the Marlins and the Rem pumps could be more easily scoped. Winchester introduced the AE angle eject model '94 to address that shortfall, as well as the more powerful .375 and .307 Win ctgs for the M94.......but I believe by then it was too late for the lever carbine as a desired deer rifle. Bolt rifles and high intensity cartridges like the ,06 and .270 and the 7mm mag, had largely taken over the market.
The M94 line needed a more powerful cartridge, but by the time Winchester got around to introducing the .307 and .375, the lever carbine's day was about done. The .44 mag introduced in the same era was not really a step up in horsepower over the .30-30 and certainly not the equal of the .35. Marlin stayed on top of the lever gun market with the 1895 models in .45-70 and .444, Winchester realized too late that the lever gun needed a boost to stay popular........now we have no blue collar M94's, new anyhow. No marlins (yet) for that matter.
Winchester nixed the powerful M71/.348, which left the big bore lever gun market to Marlin and they ran with it. I think for a big bore (.35 & up) ctg to rival the .35 Rem, introduced prior say 1975, might have given the '94 win new life, but again, Win was to late to try it.
Some type of .40, say a attenuated version of the .405, or a rimmed lengthened .401, might have been interesting. I don't think the M94 was ever chambered in a cartridge that did not have a rim.........