I'd bet on it happening during Xi's reign, as it's critical to his pursuit of legacy. He's obsessed with writing his own name into China's history, taking Taiwan (and simultaneously defeating the West as he does it) would be a very big stamp on that. It would formally signal China's new empire-like dominion over Asia.
I don't think the US will trade Taiwan as a bargaining chip. By the time the US is willing to trade it, China will fully understand it's not really worth bargaining over any longer. The time to bargain would be now, or in the recent past. If the US Government wanted to get something big for trading Taiwan, during the Trump Administration was the last time to do it (during max tensions), and the trade should have been North Korea being dismantled (as is; meaning the Kim family goes, the nukes go; only China could make that happen) and reunited with South Korea. The US Govt no doubt thinks their bargaining position is stronger than it actually is, and so doesn't think they needed to make such a trade, instead the US will get nothing and Taiwan will end up in China's hands regardless and North Korea will remain a key China pawn.