i really don't know what you are so worried about---thousands of quilters every day use poly thread to quilt their quilts- cotton thread does not work very well in long-arm machines- the machine goes too fast- the thread breaks all the time- machine quilting thread is polyester.
as for the rayon---if it was strong enough to do the job---good for you-
some people quilt with silk thread too---
it's not a problem to use the thread that works for you- and is strong enough-
the only thread i've had problems with for quilting was a number of years ago i quilted a quilt with an invisible thread that melted in the dryer---broke all over the quilt leaving horrible pokies all over it---but i do believe the invisible threads have come a long way since then.