It appears they snuck a new feature into that last patch.

 

Just got this pop-up when I encountered a dice set from a treasure chest.

 

Nice touch, guys!

That behavior has always been the case for a long long time.  

 

The popup may be newish, but ever since the introduction of dice, any set gained in excess of six was automatically salvaged.

 

The same process should exist for alternate characters if they're still in the treasure chest RNG pool.  I'm not sure what their present salvage value is (used to be half their store price in gold), but depending on the alt, duplicates may still net you 750-3500 gold.

I’ve opened a bunch of chests and have yet to see an alt. Take from that what you will

I’ve opened a bunch of chests and have yet to see an alt. Take from that what you will

 

The odds of an alt were/are super low.  Somewhere in the neighborhood of 1 in 200 chests redeemed.

 

In the process of opening those 200 chests, you'll have probably scored about 50 sets of dice.

Ahem...yeah, I may have opened more than that *sheepish grin*

 

Of course, knowing how odds work, that doesn’t mean I should have seen any, just pointing out that I haven’t.

 

Re: the auto salvage. The first time I saw that, I got gold (there was an amount shown in the message too). The 2nd and 3rd time, I did not. On my iPad, I don’t even get the animation.