By 4 years from now? A million things are going to change between now and then, many of them totally unforeseen by pretty much anyone.
If the Angels started spending money wisely and drafting well, they could easily keep Trout and have a good team before then. If they aren't going to choose good players, then trading Trout will just make them worse, and give their fans no reason to go to games or watch them on TV. Trout is always going to be worth watching, even this year when the team isn't going anywhere.
The Angels are a big money team in a huge market, they aren't going to trade the preeminent player in baseball at his age for A ball prospects. Any GM that does that is putting his job on the line in exchange for hoping on players who are several years away from even being rookies. Why would any GM do that? So that a couple years after they are fired and the team stinks and they are known as the guy who traded Trout, the team might be good again, maybe?
If you are a GM for team in that market, you are much better off keeping Trout and trying to build around him. They are in a division that usually isn't that great, so competing for a wild card spot won't take too much. The answer for them is to stop wasting money on the wrong players and start making smart small moves. They should use the rest of this year to find their own versions of Steven Wright, Travis Shaw and Brock Holt to be cheap useful pieces next year, while spending big on international free agents, and hopefully drafting better.
If they were going to trade Trout to the Red Sox, they should ask for something like Trout, Pujols and CJ Wilson for Bogaerts, Betts, Swihart and Eduardo Rodriguez and probably more. Which the Red Sox would obviously not do. If the Angels traded the biggest superstar in the game it would have to be to reshape the team to contend as soon as possible, not to start some 5-year rebuilding plan, that would get a GM fired.
The Red Sox shouldn't give them what they would need, and I don't see a trade that would be good for both teams in the real world.