China being in a position to seriously hurt Taiwan economically is not a
reason to not push harder. If anything you're saying China is in a position to take action but has chosen not to for reasons unknown.
Crimea isn't really relevant because it was taken in a matter of hours due to the shocking state of the Ukrainian defence forces and because Russia already had significant forces in the region due to its naval base. If China could do the same thing in Taiwan the US would find it hard to intervene militarily. But that's not really a likely state of affairs because China will need a serious and very obvious military build up that couldn't be hidden. The PLA does not have bases on Taiwan to draw forces from. Obama was also incredibly naive about Russia whereas Sinoscepticism in contrast is much greater now.
As for Serbia (I presume you mean the Kosovo War) NATO relied on air/sea-power which would be the US' primary military response in a conflict with China, so it doesn't show concern about the cost of war.
You're also neatly forgetting the invasion of Iraq and the intervention in Afghanistan, both of which were decried as being at risk of causing "another Vietnam". Not only did the US (and its allies) take action but it stuck around longer than anyone thought it would.
Putting HK aside, it's simply not credible to suggest anywhere near a quarter of Taiwanese could riot in favour of Chinese annexation.
"The U.S.-based Pew Research Center found that 66% view themselves as Taiwanese, 28% as both Taiwanese and Chinese and 4% as just Chinese."
4% have a "hardcore identity" as you put it, and they're almost certainly mostly in the older generation of people who came over during the Chinese Civil War. Also there were no mass riots when the DPP won in 2016 and 2020.
Even if the DPP had no clear plan, how does that change things for China? Taiwan's economy isn't stagnating, if anything it's doing much better than its neighbours right now.
I will agree with you that if China is willing to wait until after 2050 or 2100 attitudes in Taiwan may have changed such that peaceful unification with the PRC is much more possible. But waiting another 10 or so years by itself is unlikely to change anything, certainly while China keeps buzzing Taiwan militarily as it creates a feeling that there's already a military conflict going on. China's economy will have grown larger but the economic situation will be more or less as it is now. There's no magical tipping point where if the ratio between the Taiwanese and Chinese economies hits X then Taiwanese will immediately decide unification is necessary.