Here's a short video showing how mobs no longer see signs and fence gates as solid blocks, and therefore will not path off of cliffs if signs and fence gates are placed on the edge of large drops. It has implications for certain mob farming setups.
You are correct, trap doors do seem to still work. However, there is a still a problem where you cannot create a gap wider than 2 blocks that a mob will willingly walk off. Open trap doors, like signs and open fence gates, do not stop a mob from spawning in the same block, so I suppose they can work as a stopgap for some applications. There are very specific things that won't be possible anymore.
there's still always the piston and pressure plate set-ups. they take longer to build, but the advantage is that they tend not to get "broken" by updates. so its worth the extra materials and effort. a lava blade that you can toggle on and off is also a good feature to add for xp farming.
i try to keep water, signs, fence gates etc. out of my traps as much as possible for this reason.