Whaler has a 42 footer and Grady White has a 37 footer that are outboard powered. I know they aren't trawlers by any means but obviously some manufacturers think outboards are applicable to off shore, too big to trailer boats.
The Whaler has quad 300 hp engines. At WOT it burns 120 gallons per hour !!!
Nearly all builders of center consoles have outboard powered boats up to 42' and there are center consoles up to 53' now.
I had never owned an outboard in my life until a couple of years ago, not even for a dinghy. We bought a 39' Contender with triple Yamaha 300's for the use of our boating and management staff and crew. Maybe part of the reason we have a burning desire for a truly fast boat as our fastest, a Riva only hits 42 knots and the Contender can go flying past us at a gentle cruising speed since it's max is 57 knots.
I believe outboards have a place in trawler type boats, medium sized boats designed for long cruising. There are a few builders such as Rosborough and now Great Harbour with efforts up to 35'. There are others with "pocket trawlers." Sea Ray now has a Sundancer 320 with outboards. It sleeps up to 4 and has triple Mercury 250's. Perfect boat for someone wanting to do overnight cruising on a lake or river. Not really for coastal.
I don't believe we've come close yet to seeing what can potentially be done. We have small, not really seaworthy, trawler types with outboards, with small engines. We have center consoles with very large outboards and quite seaworthy. The Sea Ray Sundancer is somewhere in between. Outboards continue to grow. Now Volvo owns Sevens with up to 627 hp.
I think there are two huge potentials. First is a nice semi-displacement or even planing cruising boat with large outboards and the living platform you'd expect in a 40-50' trawler type cruiser. Second is a full displacement or semi displacement, more a Grand Banks type using outboards, probably a work type outboard design built for torque and thrust not top hp or even a diesel outboard if one shows up that is really marketable.
Outboards have taken over a large segment primarily because of price. By outfitting large center consoles with outboards, we've already seen the impact on the small sportfisherman boats. We've seen it in family boats too. Outboard have taken over where sterndrives once held.