Rather than DM (or as well as DM) how about (realtime) email – in tweet sized chunks? The main use for DM I have is that it emails you, which can be used with push email services instead of SMS (or with Email→SMS gateway for countries with free inbound SMS but not supported by Twitter SMS).

Ref: http://twitter.com/jasonsalas/status/1243812479

Love the ability to toggle IM on, DM off etc. The either or option for SMS or Website on twitter was always a limitation. Sometimes you want both. The IM off is useful if you don’t want to be bombarded with IM on a slow connection or ‘quiet time’.