Brode provides more insight.
Lead Designer of Hearthstone, Ben Brode, recently did another one of his notorious streams where he occasionally takes the time to answer a question or two about development and his design philosophies. This time around he was mostly silly and lighthearted, but did touch on the community's demands for updated quests and evergreen sets in Hearthstone.

Note: Some of these have been transcribed via Reddit and may not be the exact quotations.

Will classic set always be standard?
There are some real upsides to keeping the classic in standard forever. When you take a break from hearthstone and come back, it's a big deal to know that you can return and create a standard deck without needing every card. There's some actual value in having familiar cards in the standard format. One of the problems we were worried over was having was keeping the game fresh, which influenced the choice to nerf what we did before releasing standard.

He then commented on the post saying, "I talked a lot more about Standard and whether classic should always be part of it - I think an important point is that we are committed to making Standard fresh each year, and if that means nerfing or rotating more cards at rotation, we will continue to do that."

Can you explain your design philosophy on OTK?

So OTKs are fine if they are infrequent. Thaurissan procs for 3-4 turns are okay. Combos are great and can be very fun. I think they are very important for the game. I love the new patron warrior. Lock and load is a card that feels combo-y and is very fun. OTKs that win literally out nowhere, like bam there's 30 damage. I don't think those are great.

What are your thoughts on updating quests to be "Play" instead of "Win?"

I think it's reasonable feedback. There is a pretty big difference between HotS and Hearthstone from this perspective, though.

If you have "Play 4 games as Warrior" - the fastest way to complete it is to concede 4 times instantly. Players will min-max systems: it's important the most efficient way to play the game is also the most fun.

There are ways to get around this (The 'Deal 100 damage to heroes' quest is a good example), and I do think it's in general better to do more quests like that. I also think there is value in variance of quest types and in quests that push you to play different ways.

Sorry this is a terse response – busy day today!