Adventureland has always been one of the worst areas for foot traffic/crowds. The area in the front got better as a result of "Project Stardust" (the pre-Galaxy's edge cleanup they did in anticipation of crowds) - it used to be terrible around the entry sign, particularly if the Dole Whip line got backed up. But the area outside Indy/Tarzan has continued to be bad, though that’s usually because of people hanging out for their LL time, or waiting for rider switch, or waiting for their Bengal BBQ mobile order. Leftover strollers also cause a problem there. It's even worse once people start sitting for Fantasmic.
Hopefully they are doing some work to fix that problem during this closure, though I'm not totally sure what to do unless they move the entrypoint for Tarzan entirely and create a more clear space for stroller parking and waiting for Indy that's more out of the way. I actually think shutting this walk way may improve traffic flow in the interim - the fastest way to get from Haunted mansion to the hub was previously through Adventureland, which couldn't handle the crowd flow. Frontierland is much more spacious and doesn't have 3 attractions coming directly out of the walkway. We'll just have to see if Frontierland can handle the extra traffic.
My guess is they'll put a sign up at the entry way to Adventureland by the hub - otherwise you'll have people going in and having to turn around all the time. I expect Jungle Cruise wait times to come down a lot as you no longer get the "consolation prize" traffic from Indy (people killing time for a LL, people coming when Indy breaks down, people balking at the standby wait time, etc). In general that area should become pretty quiet which might make the Tropical Hideaway a nice place to relax.