First, I appreciate your time in responding and for the quality and tone of your engagement. I surmise you were not necessarily looking for answers (more of a "food for thought" type of response?) but I would like to (in bold simply to distinguish my answer from the question) for my own benefit in seeking clarity. I apologize in advance for answering some questions with questions:
Once again we need to ask about hermeneutics: how do we get from God appointing times for Israel's annual festivals to God appointing times for communion?
If it is necessary for God's own glory, our salvation, faith, and life, and is not expressly set down in Scripture, isn't it by good and necessary consequence to be deduced from Scripture? It is not enough for the RPW that someone somewhere in the Bible has done the thing we are advocating.
Agreed. As I noted in the OP: "I am wary of narrative-based doctrines and note that much of the early apostolic Church’s practices seemed to change." How do we know that this is a proper application?
Good and necessary consequence to be deduced from Scripture. If it is apropos, does it argue for communion three times a year, on the 14th of the First (Jewish) month (Easter), seven weeks later (Pentecost), and the middle of the seventh (Jewish) month.
When the Assembly stated that "The sacraments of the Old Testament, in regard of the spiritual things thereby signified and exhibited, were, for substance, the same with those of the New" (WCF 27.5), I infer that they are also acknowledging in contrast that the physical things of the Old are not the same as those of the New. If we add Hannukah (Christmas), on what basis do we do that?
Some see a fourth season observed by Christ in John 10:22) but we seem to be in agreement above that this is suspect: You: "it is not enough for the RPW that someone somewhere in the Bible has done the thing we are advocating." Me: "Agreed. As I noted in the OP: 'I am wary of narrative-based doctrines and note that much of the early apostolic Church’s practices seemed to change.'" The Deuteronomic bar of “at the mouth of two witnesses, or at the mouth of three witnesses, shall the matter be established” has always loomed large over my hermeneutics. Why all three festivals and not simply Passover, so that we all celebrate communion at Easter?
I am not opposed to this if by good and necessary consequence it can be deduced from Scripture at the mouth of two or three witnesses. How do we reckon with the fact that these festivals were not simply one sabbath long but about a week long?
The sabbath is not always a literal day - there is a spiritual Sabbath, and there were sabbaths not on the last day of the week (see, for example, Leviticus 23) Is that your justification for communion seasons?
Not necessarily, but it might contribute to "good and necessary consequence." How do you avoid the implication that you have just made an excellent case for Christians celebrating Christmas, Easter and Pentecost?
The Dutch Church did this (Church Order of Dort, Articles 63 & 67) as it was seemingly simpler to coopt these "holy days" since they occurred in roughly separate seasons throughout the year. The Scottish Kirk did not: "By the contrary doctrine we understand whatsoever men by lawes, counsells, or constitutions, have imposed upon the consciences of men, without the expressed commandement of Gods word, such as be the... keeping of holy dayes of certaine Saints commanded by man, such as be all those that the Papists have invented, as the feasts (as they terme them) of the Apostles, Martyrs, Virgines, of Christmasse, Circumcision, Epiphanie, Purification, and other fond [foolish] feastes of our Ladie: which things because in Gods Scriptures they neither have commandement nor assurance, we judge them utterly to be abolished from this Realme...." (First Book of Discipline, The explication of the first head.) I believe the latter is wiser because, though theoretically possible to remove the idolatry, blasphemy, and superstitions that have arisen with Christmas, Easter and Pentecost, why bother? This doesn't seem like an argument the Puritans would have eagerly embraced.
I'm not sure which argument you are referring to but no need to clarify with enough probably said at this point - I have tried to quote from those I consider the purest of redeemed sinners, and I give deference to documents adopted by the Church than individual, and to the documents of those particular churches which are more pure (WCF 25.4).