Amirsan -
I'm certain that the Writing for CB deal is contingent on our promise to research Construction. They won't trade Writing straight up for Ceremonial Burial.
Of course, we could always make the trade and then welch on our word, but good luck on us trading for techs any time after that.
While getting Writing now, is a good thing, committing to Construction will definitely mean giving up any hope of getting either the Great Lighthouse or the Great Library. Also, the more time the other civs have Map Making, the more likely that they will settle that island to the SW before we will.
On the other hand, if we can get Construction in a decent number of turns, it may be beneficial to conduct this trade. It all depends on how quickly we can get Math. The biggest discovery from the chat with them yesterday was that they will be discovering Math in 7 turns! We must beat them to it if we want to use it to trade for Writing from the other nations.
If we can get to Math first, then this trade is a no go in my opinion.