Yesterday a joint statement of four railways was issued announcing the intention of starting reserved seat service using the to-be-delivered Seibu 40000 series. Starting from Spring 2017, this service will operate weekends and holidays between Chichibu and Yokohama Chukagai (for sightseers), and weekdays, on a Seibu Ikebukuro Line-Tokyo Metro Yurakucho Line routing (for commuters). The 40000 series feature rotating seats, convertible between longitudinal and airline configurations.
http://news.mynavi.jp/news/2016/06/16/264/
press release:
http://www.seibu-group.co.jp/railways/news/news-release/2016/__icsFiles/afieldfile/2016/06/16/20160616_zasekisiteisouchoku_1.pdf