This merger or takeover or whatever adds more distribution for Authors / Publishers on Smashwords (who already re-distribute to Apple, Barnes & Noble, Scribd, Kobo, Overdrive and others).
It also adds paperback /POD, assuming the content provider formats correctly.
See
https://www.smashwords.com/united
Basically the only major online ebook seller that Smashwords doesn't re-distribute to is Amazon. They don't redistribute to Google either, but despite Playstore dominance Google Playbooks is negligible.
So uploads of ebooks to Smashwords, Amazon KDP and Google covers almost all ebook sales.
I don't know much about D2D (Draft2Digital) or their POD. The POD companies I know about are Ingram, Amazon (formerly Createspace), Lulu and 24Bookprint.