Currently in wrath classic there is no state configuration for shadow dance like there is for stealth.

With custom conditions you can have it properly working by using [form:1] for stealth and [form:2] for shadow dance.

These will add the missing state option:
{ id = "dance", name = GetSpellInfo(51713), index = 2 }, in StateBar.lua
ROGUE = { stealth = 7, dance = 8 }, in ActionBars.lua

Although in statebar.lua it would require to have a new boolean like the WoWBC one.

Does Blizzard swap automatically on shadowdance, if so where to? Is it wanted to swap to a different bar, or the stealth bar?

Does Blizzard swap automatically on shadowdance, if so where to? Is it wanted to swap to a different bar, or the stealth bar?

Shadow dance swaps to bonusbar2 according to GetBonusBarOffset(), which is a different bar than stealth/vanish (bonusbar1). To simulate Blizzard's behaviour it definitely is wanted to swap to a different bar than the stealth bar. My first post covered that, because at the moment when using shadow dance the bar does not swap at all from the main bar - not even to the stealth bar. The solution is to add a proper implementation for shadow dance, that will utilise a new bar like Blizzard's default behaviour. I hope that answers your questions.