Necro update GO! Yes, this project is still being worked on (quite a bit actually). Here's a few screen shots.
So I've taken a strong cue from SM3DW's design. Every level pretty much uses some sort of gimmick that's used through out the level over and over. Rather than apply "MORE BADDIES N HARDER JUMPS" it's "new enemy, new game concept, barrage you with new things all the time!" With that said, here's a few of the ideas that are being used:
-producer/destroyer blocks. This sort of work like the SMW conveyor blocks where one will eat blocks and the other will produce blocks. These can appear separately, have two speeds and can draw a single path, toggle back and forth on the path or have a eater/producer follow the same path.
-one block high paths no longer kill Mario. However, if you're pushed into a solid wall, you will die
-ceiling blocks extended infinitely up. Basically, if there's a block appearing at the top of a stage, if you try to jump over it, the game will act as if the wall goes up forever, so no more jumping over walls to skip chunks of levels. I did this because the alternative was produce invisible walls or coin blocks, I felt this was more natural
-Spikes now throw spiked balls that bounce along the ground and destroy bricks and stone. They will also kill enemies in the way
-Hidden Stars can dynamically show based on different conditions, such as activated P-Switch, enemies being cleared from a room or candles lit in an area
-Giant Chomps now have a "horizon" animation and fly upwards before falling down, eating away at the ground
-Chained Chomps are now tied to a block that if destroyed will allow them to bounce around freely
-Missile Mark are modifications to the homing Bullet Bills that will follow Mario in all 8 directs and explode when they come in contact of a solid wall
-explosions that destroy bricks/stones now have a 3x3 area explosion coverage
-some levels have water buoyancy, which means you will float to the top automatically. The only ways around this are either using the Frog suit or holding an item to increase your weight, allowing you to sink
-new level mechanic, rhythm based block changes. As the song is played, you will keep a "beep beep beep blip" where the blip initiates a change in what blocks are solid and not solid
-new level mechanic, timed levels where the timer starts out low and requires you to seek out clocks as you play the level to increase your remaining time
-new level mechanic, key collection scenarios. Collection all key tokens in a level will produce a key that you use to unlock a door found in the level.
-hidden coin blocks can now be hidden blocks with power ups
-subcon was redone to work like it does in SMB2. You enter a door and are given a few seconds to explore the subcon area that is one screen long and mirrored. Once the time runs out, you're immediately pulled back to the other world
And oh gods so much more I'm forgetting! As of right now I have approximately 20/63 levels complete. I'm progressing at ~1 level every 2 days and I have a beta tester going through every level and offering up initial thoughts with bug reports. Unfortunately, no release date still