Really what SE should do to help give a quick revive to old content in ToA is just add more rewards you can receive with the "currency" earned in that event. For Nyzul Isle, they could easily just add a NPC where you can exchange your Tokens in for R/Ex items. As long as the R/Ex items would have some use, something as simple as this would breathe a lot of life into Nyzul Isle.
The same goes for Einherjar too. Just add more rewards you can get with Ampoules! :/
Salvage I'm not as sure about... But Idk why SE just hasn't done something as simple as add more rewards like I mentioned above. x.x