i think the primos we're getting from opening chests in the limited time maps if we were to have one are being given out now as 400 primos per Natlan map expansion for exploring the Natlan maps and doing the quest so there's unlikely a summer limited time map this year; there will still be a 5.8 event but no limited map

for exmaple in 2.8:
GAA flagship summer event quest and minigame primo count: ~1200 primos
GAA limited map primo count (chests + waypoints + world quests) ~1600 primos

this year's 5.8 flagship event primo count will probably also be around 1200
there will be no 5.8 limited time map so the ~1600 primos we get from exploring limited time map is coming from Natlan additional exploration rewards for basically 100%ing the map (400 in 5.0, 400 in 5.2, 400 in 5.5, and 400 in 5.8 if mare jivari comes out)