Greetings, As in the patch notes it said they are thinking of new ways to earn shadow keys, Here's my opinion.
I think the Core should have boxes again. And as a rare chance in these boxes, a Shadow Key should appear given to a random party member (like gear drops, but maybe not as rare as gear drops) This will give anyone who has the skill to reach the core, there chance to obtain a shadow key for a further challenge.
Put Shadow Keys in chests at the end of arena or danger rooms. The higher the tiers, the better the chance. This could create incentive for people to explore T3 Clockworks other than FSC. If you don't get Shadow Keys, it's no big deal. The money you farmed can go towards investing into equipment for Shadow Lairs.
Bring Shadow Keys back to Boost on special occasion, like Christmas.
New Shadow Crates with 50% chance of shadow key. Shadow Crates found in Mann. Co Crates.
So a Key to open a box, to get a box,to get a key?
Its Keyception except now there's a twist zomg :O
It's like a pay per play option geez guys! There is a reason why it costs CE and why it is OPTIONAL.
This belongs in Suggestions.