There are too many possibilities to explain Stephen Roshak. A 'merger' of Jade Falcon and Wolf could be possible, but there are already multiple explanations which are simpler:
1. The Jade Falcons are ilClan.
2.The Roshak bloodname was taken by the ilClan.
3. The warrior Stephen Roshak is abtakha to the ilClan.
4. There are multiple Clans involved in the new Star League and similar to the Clan Council, the Loremaster is not necessarily from any ruling Clan but chosen for their skills relating to parliamentary order (a la Kael Pershaw).
We could speculate (and I encourage it!), but Empyrus is right. Heaps of changes can occur. Even more importantly, the identity of the new Star League Loremaster is a relatively minor plot point and TPTB have years to craft the storyline. I'm sure they haven't settled on any reason yet (or can change their mind at any time!).