Seems the shift from Android Store to Google Play did not go unnoticed, atleast not by Samsung. This one would assume by a recent development where a Galaxy user got an alert that there will be something in that end that will replace the Kobo service as the default e-Book service for Samsung devices.
The user sent the alert screenshot to Italian blog HDBlog that indicates Kobo wont be available in Readers Hub as was previously the case. Samsung has clearly confirmed that something is in the works and will be available soon. See the translated message below(Note, am relying on Google Translate here):
A new and improved e-Book service from Samsung is under preparation and will be available soon.
Users still wishing to use Kobo will have to download the app from Google Play Store.