As far as I can tell by scouring the E-Plus site, it seems that these changes are limited to postpaid customers only for the moment. The only MVNO affected by this change is BASE. None of the prepaid E-Plus plans or MVNOs show any changes yet.
E-Plus Free & Easy roaming prices:
http://www.eplus.de/tarife/12/12_4/12_4.asp
E-Plus Postpaid (E-Plus International):
http://www.eplus.de/dienste/8/8_1_4/8_1_4.asp