EDIT: In 18w48b it's still possible to power through pistons, as demonstrated in this video provided by MethodZz: https://streamable.com/yi6fc
In 18w45a and prior, pistons are transparent, meaning they don't conduct redstone power and they won't cut off redstone signals.
In 18w46a, however, this changed. As can be seen in the attached screenshots, they now cut off redstone signals and it's possible to power through them. This breaks existing contraptions and also introduces new problems (3rd screenshot. Whether the front or back piston extends is seemingly random).
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is duplicated by 2
relates to 3
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TNT, Ice, Glowstone, Sea lanterns look just like "full blocks" as stone do, but they have different redstone properties, so I don't see what point you're trying to make when you say "they should act like them" in terms of redstone conductivity.
confirmed for 18w47a
Having a block which changes its redstone transparency on a redstone signal is absolutely useless... The way it behaves will be exactly like a normal transparent block. Redstone signal passes through if there's a redstone signal. If there isn't it doesn't.

Is it still possible to power through pistons OR is it possible to power through block36 now?
(good old salty Methods)

It's just block 36.
I have up-voted this bug, but having retracted pistons pass trough redstone is a interesting mechanic. There is no other block (as far as I know) that changes its (redstone) transparency on a redstone signal. And retracted pistons look like full blocks, so they should act like them.