The Playoff Alliance Communication document is published in the Additional Season Material section of the CRESCENDO – Season Materials page
Kudos to FIRST for continuing to release volunteer facing documentation.
For people looking for quick access to it.
Curious what exactly prompted this change - trying to also rule out wheels that aren’t plastic?
Would TPU be considered a hard plastic?
To some inspectors? Probably.
This Q&A arguably goes both in depth but there have been a couple other about this style wheel.
TL;DR: TPU with a high enough durometer could count as “hard plastic” despite being flexible. This change clarifies this.
With sufficient force, all materials are flexible.
So, assuming you have 88 style wheels machined out of spring steel, how would you go about demonstrating their flexibility to a robot inspector? Asking for a friend.
Wood is flexible with sufficient water.
Watergame confirmed?
How much force you got available?
So only flexible studs are allowed? Sounds like a targeted yoga studio.
Hydraulic press, see inspector! It does bend!
Can we send our wheels to “Will It Bend?” and use the YouTube video for evidence?
Summary
Yes, I know, it’s “Will It Blend?” # thatsthejoke
“Will It Bend” would be a great name for the hydraulic press channel though… missed opportunity.
Slow-Mo Guys or How Ridiculous might also work. Especially using the latter’s axe.
Missed opportunity, or not yet taken opportunity? 
Gus’ nicknames are the best.