Sure a trijet 777X, a la 727 could be done, would it be useful, which is to say economic NO! Structures would be heavy everywhere, including wings.
The FARs and public opinion when the 727 and the heavy tri-jets were also an important factor in addition to engine power. In the sixties, there was a strong bias against twins, take-off weather requirements in 121 were a big element in Eastern and United wanting a tri-jet 727. Twins, I don't believe, could use low mins and a take-off alternate, they had to have a mile viz or landing minimums The "public", meaning media and opinion thought flying across the US, let alone oceans, demanded four engines, going to three was a leap of faith. Privately, the engineers at the airlines were reluctent to buy less than three for long-range in fear of the public rejecting them. Remember airlines were moving from Connies and DC-7s, so everyone associated flight with FOUR engines unless you were puddle-jumping in a Convair or Martin. We forget now that in mid-Eighties, going outside of 60 minutes with a twin was a "there they be dragons" kind of operation.
Hell, getting down to TWO crewmembers was a real effort! The original 767s had an F/E.
GF