With the WTO, the World Trade Organization, the People's Republic of China joined first and then Taiwan joined almost immediately afterwards, although Taiwan had been compliant way before the People's Republic. Possibly, that would be on a track with TPP.
Taiwan has signed bilateral trade agreements, I think with Singapore and some others. It might be politically possible, but I think there may be costs. It's a complicated issue. There may well be costs.
If it's a big deal, you can have Taiwan as part of it, but how can you exclude China if you want it to be meaningful? It's so much bigger as an economy.