Yes you can take them with you, though it hasn't been said how you will be able to upgrade them. http://planetdestiny.com/taken-king-gameinformer-review/ [quote]"Of course, our Exotics will be with us always. So fear not, your No Land Beyond is safe – wink." [/quote] In addition this was on planet destiny too: [quote]“As an alternative to using or sharding your new high-powered Legendary weapons and armor, you can also improve an item you like by sacrificing another piece from the same gear slot.”[/quote] So our old legendaries might not be so 'obsolete' if they are indeed used to up the power of new weapons or even rip certain perks out of them. But it'll probably only apply to new weapons.