These are some things that can be done to stop pvp from dying (and save the server)
1. Stop focusing on Regalia
This is by far the biggest elephant in the room. Everything that is done in terms of updates is geared towards the roleplayers in regalia, neglecting pvp and factions. I don't understand what happened that caused staff to focus regalia, but know that this is not the way the server should go. When this server started, to my understanding, it didn't want to be a roleplay forum in 3D. It was the creator of factions after all, isn't that what you are so proud of? This server has tremendous potential to deliver a real Game of Thrones experience, where roleplay and pvp mix beautifully. This server was about big kingdoms, fighting eachother for power or by using diplomacy. Over time this vision was lost and regalia became the focus. This is what we strived to do with Byzantium, having a big faction empire that's actually an empire, based on the real life Byzantine empire. Why don't you focus on creating an experience, where there are kingdoms greater than Regalia, fighting eachother? That is real.
2. Stop banning PvPers for petty shit
This one is obvious. A lot of pvpers have been banned for the pettiest reason one could think of, like (sometimes even accidentally) saying "dance" in general chat, or disrupting some event. From a business perspective, this is suicide. Why would you ban someone who is actively playing and contributing to your server and the factions experience for saying dance? Why would you permanently ban someone for "disrupting" some non pvp event, while you could just jail them or remove them? Tell me, how are you improving the quality of the server this way?
3. Moderators being too strict / not understanding the nature of competitive gaming
A bit of a continuation on 2, it is obvious to me when a mod clearly isn't fit to regulate a PvP server. People flame and insult eachother not because they hate eachother, but because it is funny, and adds to this competitive feeling. No one gives two shits if they get "insulted" by someone they have been fighting with, it's just part of the experience and makes it feel a bit more real, a bit more alive. Don't want the more casual people to see it? Bring back PvP chat, and allow insults. Again, no one cares if they get insulted, and if they do, their heart probably can't take pvp and losing stuff. Why did Pvp chat get removed in the first place? That's just dumb, considering general doesn't allow someone to get something off their chest (of course, not in a totally savage way, that is common sense). Insulting eachother is part of the pvp culture, only needing regulation when things get too extreme.
4. Encourage people to take an initiative
Much can be done here. Get someone like Mafro to create a youtube series functioning as a tutorial, make grinding easier, tell them about schematica, inspire people to realize their dreams of being a king over a feudal country. Many suggestions have been made for this, and I think they are all good.
5. Turn old pvpers into moderators
This is a nobrainer. These players know the server probably better than the admins (from a player perspective) and a lot have done much for the server already. Drop the requirement for having a clean record; when you respect someone enough to give them a position where they can help out the server they love, they will respect you back. For a pvp moderator, you need someone who experienced the pvp fully. Having roleplay moderators and game moderators is fine, or we make every moderator less strict to flaming / insulting / disrupting some event. (Not jabbing at moderators individually - it's just that your job is not suitable for pvp, and you aren't the ones creating the rules)
All in all, Massive has the potential to be Kohi faction / HCF but with a more real life feel or a more fantasy feel, a more empire building, grand feel, that is more than just PvP. Building, cultures, art, anything you can imagine. Once something as perfect as this gets a bit of a reputation, I guarantee that the servers will be full every day.