Far more likely eventually to arrive on the eastern coasts of Madagascar, Kenya, Tanzania, or Mozambique. My guess is that, assuming it is from MH370, it was one of many floating objects. If funds and resources were available, those long coasts would be the areas to search.
Having worked in southern and eastern Africa for years, let me tell you that any bigger piece of debris would be re-used. A flaperon makes a perfect piece of roof, seats are, well, seats, etc. People living on these shores are *very* far removed from the internet and the goings-on in the world. I am reasonably certain that there is more debris being washed ashore, yet it will most likely never be identified or analyzed. What would be needed now is an awareness campaign (together with financial reward) along these coasts. That the flaperon washed up on Reunion, which is French and therefore rather well organized, was pure and utter luck.
but is the concept of a glassy sea plausible?
In one word - nope.