Hey everyone,
Thanks for voting! We have successfully sourced and dropped the Audio-Technica ATH-M50x Headphones in the past: https://www.massdrop.com/buy/audio-technica-ath-m50x-headphones. Due to the overwhelming number of requests, we're looking into another drop for them, but it's still a work in progress.
As for Sennheiser, we have spoken to our vendor and unfortunately, they are not doing any more drops for the rest of the year.