I like your idea but see one small snag. My alt is still in Season 1 so should they only be able to get season 2 heroes?
It is annoying they keep nerfing heroes right after they get maxed and you cannot retrieve the resources used but two of my strongest heroes are season 1 picks.
Perhaps there should be a daily summon for each season and you choose which one to use but you have to be past a certain level in that season to access it?
you could still buy offers from the store with the designated portal coins, for example, you can buy 10 season 5 summons for 10$ and with my suggestion, you would receive only season 5 heroes.
The question of a season summon giving heroes from different seasons has been raised before so having season coins that summon ONLY that season hero makes sense, however we get the coin.
It seems to me they don’t want new season heroes flooding the game so sort of limit would make sense.