If the government were defeated before the bill received royal assent, the measure would obviously no longer apply. The capital gains inclusion rate would therefore be 50% for everyone.
As for the fact that the bill to implement this measure hasn't yet been introduced, and that it was the subject of a notice of ways and means motion separate from the rest of the budget content, this is a bit unusual for such an important measure. I can understand that it's probably technical issues that are still preventing the bill from being introduced. However, given the nature of the measure, we would have expected the legislative drafters at the Department of Finance to have drafted the appropriate amendments and published technical documents much more quickly, rather than what we've seen in recent weeks or months.
In summary, there was the announcement of the budget, then the notice of ways and means motion several weeks later, and then another revised notice. This sequence of events is a bit surprising.