Why do you guys think the playground is an inconsistency/retconn? The beginning of the opening focused on the upper plate but ended with a shot of the playground in the slums before transitioning into the original opening. There's no reason to think it's before the plate was built or is on the upper plate.
The shot of the playground in the trailer looked like someone on the bottom looking up at the reactor, surrounded by the upper plates to me (that's what all the houses and bridges up above are, aren't they?). It's not like every square inch of the slums is covered by ceiling. There are gigantic gaps between each sector/pizza slice (at least the width of a reactor), where the reactor is in view, and that's just about where I assume the playground is, right?
Here's a visualization:
Pizza Slice #7 (covered by upper plate that comes down):
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REACTOR ---------- Empty space between 2 slices (no plate above, natural light can reach slums from here) ------------ SHINRA TOWER
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Edge of Pizza Slice #6 that's right up against the empty space, directly in view of reactor, only partially covered by plate, partially lit by natural light
^
|
<--- Little girl is looking this way at reactor after coming down slide
| Climb to Shinra tower this way --> |
[TBODY]
[/TBODY]
Deeper into pizza slice #6 (completely covered by upper plate):
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REACTOR ---------- Empty space between 2 slices ------------ SHINRA TOWER
(I assume this space is why Aeris' house is bright and sunny)
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Makes sense, doesn't it?