Something I had pondered suggesting previously was adding in new solo instances within old zones from your home Alliance that only unlock for veteran (level 50) players.
These could continue/build on older stories or start a new one, like the veteran versions of group dungeons do, possibly bringing back old characters. Maybe 1 to 3 larger dungeon sized instances for each of the five major zones. And with the new scaling, they could fit whatever level you are currently at.
On the plus side for devs, it's easier to work with than building whole new zones and creating all new stories and characters. On the plus size for players, more immersion in familiar settings. Maybe a one-off (funny, light) and one cross-zone coherent story plot instance per each of the five major zones.
Off the top of my head, it could look something like this for the Ebonheart Pact to use on Alliance as an example:
Sample Quest Excerpt[When arriving at a wayshrine in a Pact Zone, at the North or South Morrowind Gate in Cyrodiil, or an Adventure Zone upon reaching level 50]
Non-descript NPC with a new quest indicator: (speaking quietly when selected)
"Pardon me. Forgive my clumsiness."
<She slips something in your pocket as she bumps into you then quickly walks away>
Quest "A Secret Rendezvous" is started; quest description:
I should check my pocket.After using the Cryptic Note from your quest inventory
"Hey hero. Meet me as soon as you can in Mournhold. Somewhere dark and dangerous. You know the place."
Quest description updated:
This sounds like Naryu. I should travel quickly to Mournhold to see what she wants.Upon arriving in Mournhold, quest arrow now specifies an entrance to the city sewers
Upon encountering Naryu in her Morag Tong outfit, quest "A Secret Rendevouz" is completed. Quest description is updated:
Speak to Naryu.
Upon selecting Naryu:
"Hello again, hero. It's been a while. Our mutual acquaintance Thrush wanted me to reach out to you as soon as possible. He's been following your exploits and is quite impressed."
Player option: "The head of the Hidden Armigers?"
Player option: "How have you been, Naryu?"
Player option: "Goodbye."
"Yes, the one and the same. You recall the business with the Covenant on Bleak Rock a while back? It turns out there was a reason why their invasion force risked exposure for a detour to that frigid island paradise. The Armigers have uncovered evidence that agents from the Ring of Daggers were behind it. They were looking for something and willing to endanger a major military operation to find it."
Player option: "Do you know what it is?"
Player option: "Goodbye."
"Of course not. 'Need to know' and all that. But I can say that the Covenant forces holding Bleakrock have gone quiet.
The Pact is planning an assault to retake the island and deny the enemy a base of operations so close to Stonefalls, so the naturally Armigers have been tracking all communications to and from the the island. There was a coded message believed to be related to whatever it is they're searching for, then everything went dark.
The Armigers are stretched thin, which means they are looking for reliable agents with a proven record in assisting with vital missions for the Pact."
Player option: "Why didn't they ask you?"
Player option: "I'm not interested."
Player option: "Goodbye."
"They did. The Morag Tong was offered a very lucrative contract for my services. But I've been hired to run down other leads, and what they need on Bleakrock is more suited to someone of your particular talents. So are you in?"
Player option: "Of course."
Player option: "I'm not interested."
Player option: "Goodbye."
"I knew you wouldn't be able to resist, hero. Look up Sala Bitterbone at the docks in Davon's Watch. She has a skiff that can get you to your destination discretely."
A new quest, "Back to Bleakrock", is started. The description suggests:
I should find Sala Bitterbone at the docks in Davon's Watch.
The quest continues when you meet Sala and confirm you wish to continue. You arrive at a remote corner of Bleakrock that is separated from the rest of the island by slaughterfish. You are then told a bit more about what you are looking for, and to proceed you have to jump overboard and enter an underwater cave passage. Once through the passage, normal control over your character resumes and you immediately notice all of the bodies....
Whether the Daggers continue to be the villains after finding what they were looking for, whether someone else took it from them, or whether "it" killed them when unleashed, this starts a series of quests full of intrigue and familiar places and faces that takes you from Bleakrock to Stonefalls, Deshaan, Shadowfen, Eastmarch, and The Rift, though not necessarily in that order. Not sure when/where I would use Varon Davel, but I'd hope to see him again as well with more of an expanded role.
As for the light/funny one off level 50 instances, one of them would have to include Rigurt the Brash. And it might be interesting to see a more complex quest involving an old business associate like Naril Heleran.