There is a suggestion by many that the WTC finals should be played in a three Test match format and hopefully we will see that in the future.
How can a final consist of 3 matches? And in case of test tournament, that would mean that the final will be played out over a duration of one and half months. It will be just like any other bilateral series and there won't be any excitement. It doesn't make any sense. Let it be limited to one match. If not, there will be new requests to change the format of the ODI World Cup final as well. I would suggest adding one reserve day for the test championship final. But having a three match final is not a good option, IMO.
I totally agree with @Vishnu.Reang. If the WTC final is played in a 3 match format then it will not feel like a final match. The audience will not feel any excitement. It will seem like a general test series held between the two countries. So without formatting 3 matches, it is enough to have a match final.