As Näamah said here, the constant push of the required level to queue these events should be stopped. All of the season events and in my opinion, even all TW queues, should be available at level 15 when RDF is available.
The bosses are a joke, and it would remove a lot of the friction from players not having to level their alt army each year just to do an event dungeon for a drop that should have been dropped years ago.
Removing the instance cap together with an account-wide first of the day buff would remove any reason to do it on alts, which is also something that I think should be looked into.