Go ahead and do song dragon 2 and take the Wyrm of War archetype, which we'll say converts the spellcasting so it stacks with wardancer martial progression.
Just to let you know, I'm going to write a few Wardancer ACFs today, one of which will grant Divine Muse.
Awesome. So here is how the archetype is written:
A DM using Tome of Battle might instead give wyrms of war access to maneuvers and stances from the TigerClaw discipline. Treat the dragon’s sorcerer level as his initiator level when determining known and readied stances and maneuvers. To learn a maneuver or stance, a dragon must permanently sacrifice a sorcerer spell slot of the same level.
Oslecamo's song dragon class says this:
A Song dragon receives spells known and spells per day as a sorceror of 2/3 his level, but he has CL equal to his HD.
So I think the way I'd interpret this interaction is that:
1) A wyrm of war song dragon's racial hit dice stack full for determining initiator level.
2) A wyrm of war song dragon's racial hit dice only stack for determining when you get new maneuvers known/readied and stances at the levels indicated in the chart.
So if I started out as a Song Dragon 1, then took 3 levels of Wardancer, and then took another level of Song Dragon, I'd be able to pick up a 3rd level stance with that last level, because my IL would be 5, but I'd be choosing a stance as if my Wardancer level were 4 for the purposes of progressing maneuvers known and readied, and stances known.
If this is OK, I'm quite happy with that result.
I'm not sure what we'll do if I ever hit levels 7 and 16, though:
Domain: At levels 7 and 16 the Song dragon can add the spells from one domain to his spells known list. The choices are Healing, Travel, Trickery.
Maybe I can just trade out the domains for a Devotion feat.