I don’t think it is a real problem, nor would this be a solution in my book. I think if they create 6 star heroes this late in the game, they will have a lot of the higher ranked players quit. Apart from that they would also need to come up with new ascension materials with even lower drop rates etc. etc. Not really a route I’d like to see this game go to be honest.
The current storyline has been finished with at least full 4* teams, I believe some people have been able to do it without even that. In my opinion the new season shouldn’t start off the same as this one (I mean, by the end of it will we be paying 30 flags to play one level?) and part of it should just be for the story. They could still make it an awful lot harder, even up to the point where you need a team of maxed 5*s and battle items to finish it (so also a lot harder than last stage of advanced event).
To make it worthwhile for people to play and to keep interest they could change lootdrops on the harder stages (3* heroes, battle items, avatars, ascension mats that aren’t currently on the map, or even let you unlock whole new functions such as ‘practice raids’). Not saying I’d necessarily be in favour of all this (please let us all have practice raids/titans now :’)), but there are plenty of new heroes released already and adding a new star layer would do this game in for me.