I'll preface this by saying I was never especially bothered or moved by the non-religious use of "Advent of X", for better or for worse. In fact, my remark is inspired only by your comment, concerning its consistency and who has the stronger case.
Specifically, while it is true that certain kinds of words can become decoupled from their original meanings (which is generally normal), in this case, the usage is not so decoupled, especially given that this usage occurs during the religious season of Advent and with the intentional allusion to the religious season of Advent. (Otherwise, what is "Advent of X" without its religious origin and which takes place at the exact same time during the year?)
You can make a much stronger argument that the non-religious usage is a kind of cultural appropriation. That would make your concern entirely backwards. Your wish is to keep it "neutral" to please those who don't practice Advent, as you show a simultaneous lack of concern for the tradition it appropriates from. This involves a tacit claim of possessing the authority to do so as well, but if anything, given the source, if anything, the authority belongs not to the appropriators, but to the Church.
One wonders how a "Ramadan of Code" or "Teshuvah of Shell" would be received.
"Neutrality" is, of course, a bunk concept, and the idea that we ought to be guided by what is "nice" rather than what is "good" is a grave misunderstanding of how decisions ought to be made.
