The tri-jet concept (except for the biz-jet set, IE: Falcon) is dead as a doornail....for airline aircraft, IMO.
One must remember...the L1011 started design life as a twin, but was 'upgraded' to three engine status, as the available engines (at the time) were insufficient thrust.
Twins are the way to go now, in most cases.
Keep in mind that my entire jet flying has been in three or four engine types, which were the way to go...in past years.
Not any longer, however.
NB.
We have one specific contributor here, who was involved with the initial L1011 design and certification (glhcarl), and perhaps he can provide further comment.
One thing is for sure, however (regarding the L1011 design), two now retired Boeing design engineers told me personally that when they had a first close look at the L1011 avionics design, they admitted that Boeing, at that point in time, were 'waaaay behind' in systems automation.