The obstacle is evidential rather than interpretive, which is why more argument has not helped. Three kinds of evidence would in principle decide the question, and none is available in usable form.
The first is the rite itself. Srauta performances of the soma sacrifice have continued into the present, but what they press is a prescribed substitute, chosen because the original was already unavailable when the ritual manuals were compiled. The living tradition cannot report a plant it had lost before it began writing the rules down.
The second is the text. The hymns are poetry composed for ritual use, not description composed for identification, and their imagery has been read in support of every candidate proposed. That an argument can be constructed from them for a mushroom, a shrub and a herb alike is a fact about the source rather than about the plant.
The third is the ground. Securely dated botanical residues from a vessel used in the rite would carry the question, and claims that Central Asian temple deposits provide them are contested on both dating and identification. Until material of that kind is recovered and independently confirmed, the identification remains unestablished. The atlas records the study as inconclusive and keeps the fact it supports marked accordingly, because saying who tried and what would close the gap is more useful than a confident answer nobody can check.
Sources Soma: Divine Mushroom of ImmortalityR. Gordon Wasson with Haoma and Harmaline: The Botanical Identity of the Indo-Iranian Sacred Hallucinogen and Its Legacy in Religion, Language, and Middle Eastern FolkloreDavid Stophlet Flattery and Martin Schwartz, Soma and Amanita muscariaJohn Brough