There are 6 more months before Valhalla storyline ends. And I bet there will be new Valhalla heroes released every month. That is why i am hoarding my valhalla coins and spend them by December as all Valhalla heroes are already there than spending them every month only to get the same heroes.
Might be a good idea to follow the Topics tagged beta-beat hashtag, so you can be informed of news directly about new heroes who are beta-tested.
But it seems extremely likely that there will be new heroes in the future. though probably too early to tell how many will be 3*, how many 4*, and how many 5*โฆ I also hope there will be more new 3s and 4s.