Bloodthirster for mages

So AP itemization changes are on the horizon, with that, it would be fun to discuss possible items that could be interesting for mages.

I've had an idea for an equivalent for a BT, but for mages. and no, i'm not talking about spell vamp.

Blast Converter: 80AP 300health Unique Passive: Magic damage you deal is converted into a shield that lasts for 6 seconds and starts degrading after 3 seconds. 30% of magic damage to champions is converted into a shield, and a third of that value from minions. Shield value cannot exceed 50-300 + 50% AP

A shield would help mages survive damage, while not allowing them to have infinite sustrain. It would reward mages for dealing damage to champions, and would be much more interactive than the passive and uninteractive lifesteal that adc have that gives them infinite sustain.

ADC have lifesteal

Tanks have warmog

AD champs have death's dance

I think a similar AP item is much overdue.

Also i know that Hextech Gunblade offers sustain, but it's stats are wasted on most mages, and it's basically useless on AoE champs. Blast Converter could allow mages with AoE to still get defensive value out of their damage dealt.