For practicality, electrification is probably the way to go. I hate it, but the point of the LIRR is to provide commuter service to an expanding number of residents. MU cars are a fact of life and practical, due to the "non-turning" issues, lack of pollution, simplicity, and capacity.
What I'd like is aesthetically pleasing, but not practical. I'd like steam locomotives and steel cars. I'd like FM's and ALCO's in original paintschemes. I'd like turntables and wyes at the ends of the lines. Unfortunately, that isn't going to improve capacity, timetables, numbers of trains, and numbers of riders.
What we must never have is abandonment or shortening of any tracked lines to any communities on the Island. Long Island is an entirely different place for what it was when I was a boy in the 50's. Then, it was all potato fields and housing developments springing up where afew farmers sold off their holdings. In the 60's and 70's, open property began to fall to urban sprawl, and rich "Yuppies" headed out to the east end, feasting on the last elegant land on the Island, and having "flash in the pan" celebrities as neighbors. It's only going to get more crowded and require more service. The LIRR is going to have to be there, operating at a loss, charging more, and retaining little of the appearence of the old company.
Eventually, expect to see EVERYTHING electrified, excepting the extremes of Greenport and Montauk. On those runs, expect to see something akin to those double-ended monstrosities that run today. The change is inevitable, but not enjoyable. I hate reality as much as anyone.
"We no take-a gasoline. We no take-a airplane. We take-a steamship! And that friends, is how we fly to America! - Chico Marx