Would calling United desk help (HUACA)?

Just adding another data point below for what is worth.

I had an ECONOMY award flight booked for ATH-EWR under YN using 70K miles. I reached out to United on twitter to be waitlisted for saver Business class award and this is the response I received:

Thank you for verifying. We've looked into this, and we are unable to waitlist for Saver Business class on your flight from ATH to EWR on August 21. We'd like to let you know that we can no longer process waitlist requests for Saver Business Award in "I or "IN" booking class. We have shifted to dynamic pricing where at any given time, the mileage requirement may change, unlike before when every travel region has a fixed mileage requirement.

Upgrade waitlist request for award bookings is only applicable if originally booked in Business class (mixed cabin), where miles have been deducted accordingly, but the appropriate "I" booking class is not available when the reservation got ticketed. ^DO