I too am surprised that they are publicizing Subala, his wife, Drupada. At this point in the serial, Drupada's only major roles were his insult to Drona (will probably happen in flashback), his battle w/ the Kauravas & Arjun, and later, Draupadi's swayamvar. After that, he'd just play cameo roles in battles b4 he gets slain on day 14.
Subhadra's role is an elastic one - they can magnify it by expanding her time w/ Arjun once she marries him, showing her raising Abhimanyu during the exile, welcoming Uttara after her marriage, comforting her after his death and being her companion from that point, being there @ the birth of Parikshit. If they go as far as Swargarohan, then she has an important role - when the Pandavas retired, Yudhisthir & Arjun left her in charge of Parikshit & Vajra.
So they can show as little or as much of her as they like. Given that it's a well known face Vibha, I hope they maximize Subhadra's role in the serial - she's one of my favorite characters.