Here is a list of all vaulted items, color coded by how recently they were vaulted.

Personally I would prefer the combination of shorter unvault periods and more unvaults, even if that meant only one warframe at a time. An item enters the Prime Vault means that players are no longer able to obtain Void Relics that can reward those items. Before Volt Prime goes into Vault: Rhino (january 2016), Loki, Nyx and Nova. Prime Access change every approximately 3 months, so you can do the math.

So Volt maybe in 2017 Limbo will become the 20th warframe to go into the vault (not counting Excalibur Prime), so even if we had an "unvaulted warframe of the month" it would take +1,5 years to go through them all, once. The Prime Vault, an archive outside of Tenno reach, houses items that have been retired from the game's reward tables. Any relics, blueprints, and components that the player already owns will not be removed from their inventory if they are to be vaulted. Find the best missions to farm relics.

Find out which relics you need to complete your prime sets. Also there’s a pattern of releases being two males or two females in a row and then alternating. Below you can see the suspected Warframe prime release order schedule.

"An item enters the Prime Vault" means that players are no longer able to acquire Void Relics that can potentially reward those items.

Warframe Prime Vault is an archive outside of Tenno reach, houses items that have been retired from the game’s reward tables. Look up ducat to platinum pricing ratios. Someone mentioned that they cry when newbies aren't aware what is in the Prime Vault and don't choose a vaulted item. Typically it’s around 100 days between every prime release so the next prime comes out roughly every season.