As a lifelong Cubs fan (since the Sandberg days) I definitely cannot see this happening. With all the renos that happened in Wrigley since 2014, doubtful they look to build anything in the foreseeable future.
I assume the same for Fenway as they did several renos up to and including this year. Too much reverence and too much money sunken into to both stadiums. Granted it is a bit trickier with Fenway's configuration than Wrigley's to keep renovating but honestly cannot see it happening.
Doesn't mean it's impossible but highly unlikely in our lifetimes.
Chicagoans have also been burned before and probably wouldn't want to see another abomination like Soldier Field happen to Wrigley. What a sad result to such a storied place. Perhaps in another 40-50 years, some wrongs can be righted there.
Sure, each could build new parks with almost exactly the same field dimensions like the Yankees did. Both would have to be very careful about seating as a lot of Yanks fans were/are NOT happy with the current layout. BUT one of the biggest issues at least with the Cubs is the neighbourhood that has incorporated the ballpark into its culture. Also the fact that the owners (Ricketts family) bought up lots of the adjacent buildings and most of their fortune is tied into the Cubs and that aforementioned real estate. Just plonking a stadium in some vacant lot next to a highway with the same dimensions as the old park does not necessarily a great experience make.
Assuming the same would be true for the Red Sox but I don't follow them as closely.
Again comparing the New Yankee Stadium experience, the Yankees built a block away on a public park so no real change to the neighbouhood, not that it's really the same as Wrigleyville.
The properties the Ricketts' bought surrounding Wrigley are nowhere close to the footprint needed to build another stadium. Maybe a shared few seasons in whatever the White Sox call their stadium could house the Cubs during a rebuild. Maybe.
As for the Halos, it's really anyone's guess. Doesn't have the reverence that Dodger stadium has in LA. I'd also love it if they could go back to calling themselves the California Angels.