Could my EB-5 visa processing time change if I change my citizenship?

Unfortunately it will not change anything if you gain another citizenship. Your friend is correct, it is based on birth country unless you are married to someone who was born in a different country.

Processing depends on where you were born, not citizenship, but if your spouse was born in another country you can cross-charge to that country for your priority date.

It is based on the country of birth. Otherwise, there would be a lot of new marriages or new citizenships for backlogged investors in the past few years.

It is correct that the waiting line is not based on citizenship but place of birth. If you entered into a legitimate good faith marriage to someone from Taiwan, for example, and they applied together with you, then you are out of the China quota.

The country of chargeability for immigrant visa number allocations is the country of birth, not the country of citizenship.

Change of citizenship now should not change the queue because the queue depends on the info on I-526 and it is too late to change your information when it is already approved.

Your friends are correct, partially (which is pretty decent for legal advice obtained from friends). Obtaining another citizenship/passport will not speed up the process. You could get your EB-5 based green card faster through a process called cross-chargeability, if you marry someone who was not born in China.

No, it depends on the country where you were born. You cannot change that!