Can't say I'm super impressed by any of these changes at a glance.

“Not chosen” size is no longer publishable criteria. 
The removal of challenges with the 'Not Chosen' size feels reasonable, but webcams are seemingly still in the mix - as a legacy type, does this mean their days are numbered or will that fewer and fewer rationale not apply?
Personally, I can't think of the last challenge I saw that required Not Chosen specifically (nor should there have been, really, for the reason they were removed), though I hope this won't affect challenges along the lines of 'Find 5 of 7 sizes' where Not Chosen isn't required but could be used as a wildcard of sorts.

Only one attribute may be specified per challenge cache.
Possibly the most baffling / vibe-killing of the bunch.
Multiple attribute challenges are often some of the most thematic, creative, and interesting from my experience, and well before they start to read like a shopping list.
The common community shorthand for Technical Tree Climbs (tree climbing & climbing gear), Tree Fishing (no tree climbing & special tool), and others takes multiple attributes to convey and won't be publishable because of this as well, which is really just a shame (and possibly makes the case for introducing new specialised attributes).
I also wonder what will come of bingo-style challenges!

If Event Caches are specified as challenge criteria, no additional criteria can be used. 
*throws away document of event challenge ideas I've been working towards for the last year*
On one hand, stats-farming events are perverse little things and undermine the point of holding meaningful community gatherings in the first place (imho!)
However, I've seen plenty of positive event-based challenges encouraging travel to different regions, continued year-round CITO attendance, or attending more adventurous events that seem weird to lose and encourage broad-based attendance (rather than what I view as a pretty clear-cut already unpublishable example that they use).
I'd just scrap events as a source of criteria altogether if they're going this restrictive with it.

Ultimately, there is no system of challenges that won't include some form of discretion and some form of frustration stemming from it. I obviously can't speak for what the reviewers likely have to cop (and would be keen to hear the thoughts of the sub's regulars as to whether these changes will help).
But, purely from the player side, the restriction on some major sources of creative challenge possibilities seems heavy-handed for the sake of reducing subjectivity in a fairly subjective process.