The question is can the ROC cough up money for both a multi-billion dollar upgrade and the new F-16 purchase? Looks like one of the other services will have to be cut.
Taiwan isn't going to get any subs, unless they get refurbished LA class SSNs.
They have known the block 20s will need upgrades for years and there was discussion with Pratt a few years ago already on engine upgrades, probably more a -220P upgrade than a total replacement with the -229. They also want the block 50s to replace the F5s, so while both programs may not happen concurrently, they will happen as buying enough new planes to replace the block 20s will definitely not happen for a long long time!
Nuclear subs will never happen. I think they would be quite happy with a few SSKs, maybe GD can buy those Greek type 214s which haven't been delivered. DCN and Thales owe Taipei almost 3/4 billion $ according to that recent tribunal decision over the Lafayette "commissions". They obviously aren't likely to pay that, or even have that sort of cash to pay out, but they do have something of value to that order that Taipei wants, like the Skorpene design. GD Electric Boats could no doubt come up with something very functional very quickly for Taipei if they start with the complete Skorpene design as a starting point!