Response to last sentence: No.They can't - just like a normal swordmage, if they use aegis of X again, it removes it from previous targets marked by that power.
"The target remains marked until you use this power against another target."
At the end of the day, is there any particular reason to encourage the hybrid swordmage _not_ to take double/total aegis?
Response to first sentence - "Ah, makes sense".
I think I got confused by the post upthread when Ferghis said "the benefit of this feat to a hybrid swordmage is significantly greater than to of a non-hybrid swordmage", and that "A common (and well-discussed) tactic for paragon-tier hybrid swordmages is to try mark at least one minion each time so that they can quickly recover the power and mark more enemies."
I gather the "mark more enemies" simply means "keep two enemies marked" - in which case, the use of minion-marking seems unnecessary - if you mark two non-minions you'll still have two enemies marked.
And I also then don't see the feat's benefit to the Hybrid being signficantly greater. I guess you can make your Hybrid Aegis more flexible than it otherwise would be, by always trying to include a minion and hence having a "handy Aegis recharge" option. But a non-Hybrid already has that option, in virtue of Aegis being at will for them, and can keep two real targets marked at all times. Whereas a Hybrid who goes for two real targets loses the minion-based flexibility.
Or am I still missing something?