当然无法预测六年后的税法，但是根据现在的税法，这么算。

Requirement, you can claim primary residence exclusion only if you lived at the property 2 years out of 5 years before the sale. 

In your case: 

Total years of ownership:  2032-2004 = 28

Total years of primary residence: 2008-2004 + 2032-2030 = 6 

Total years of rental:  28-6=22

Therefore, for your capital gain at 2032, 22/28 has to be taxed.  and 6/28 can claim primary residence exclusion. 

For example, if your capital gain is 280K, you have to pay CGT for 220K.  

But if your capital gain is a huge number, and if 6/28 x capital gain > 500K, you can only claim 500K.