It's possible that part of the law that stipulates releasing the presidents in the order that they served is interpreted to mean we can't skip Carter (if he doesn't die in time) to honor Reagan. If so, I can't imagine a Republican not introducing a bill that amends the law to get Reagan on a dollar and I can't imagine a Democrat voting no. OK, maybe a couple...
That is how the mint has apparently interpreted it. Their list of issue dates for the President dollars ended at Nixon until Ford died even though Reagan was already dead. When Ford died they updated the list to include him, but it still doesn't include Reagan.