Rashi on Amud Aleph (“Tolin”) speaks of a halachic question that the Gemara decides will wait until “Eliyahu Hanavi comes and answers the question.” The Maharitz Chayes on our Gemara raises a question. Rashi himself in Shabbos (108a, “mai”) states that we do not look to Eliyahu to resolve halachic questions, as “the Torah is not in heaven (Bava Metzia 59b).” We only use Eliyahu to resolve practical factual questions. (Also see end of Mishne Lamelech, Ishus 9:6.)

The idea behind this is that facts can be resolved by prophecy but Torah decisions are not facts. A Torah law is a judgement and application of Torah principles which are voted on through the Sanhedrin’s legal process and can vary based on the subjective judgment of the sage. This is a fundamental idea about what makes Halacha.

By way of metaphor, a school or society could have a guiding principle, “we do not discriminate against any race.” Then, there may be several laws that are enacted to uphold this principle, sometimes affirmative actions and other times, prohibitions. So too the Torah has principles that are eternal, but applications of these principles will depend on factors that the judges decide at that time. (See Rambam, introduction to commentary on the Mishna.)

The Chasam Sofer (Likkutim:98 “aval”) makes a distinction between a vision or manifestation of Eliyahu and his coming presence at the time of redemption. When Eliyahu manifests himself now, he is as an angel and therefore the experience of a sage who is taught by him is akin to prophecy. However, in the times of the Mashiach he will be reincarnated into his body. He will then teach and offer Torah opinions as any Torah sage, and it will be a valid, human subjective judgement. I found support for the Chasam Sofer from Rashi in Sanhedrin (51b, “Hachi Ka-amina”) who also seems to hold that the Messianic era is one of a resurrection where we will ask Halachos of reincarnated sages.

Two other answers occur to me:

There is a tradition from the Arizal (Sefas Emmes, Korach 5647) that in Messianic times, the halacha will be in accordance with Beis Shammai. Tzafnas Pa’aneach (Shemos 7:4 and Terumah 1:32) explains the disputes of Bais Shammai and Beis Hillel as having to do with accepting certain pragmatic realities versus the ideal. That is, Beis Shammai represents an ideal, and Beis Hillel represents a more pragmatic approach (also see Malbim Devarim 29:1.) This is why often Beis Hillel is the more lenient approach and Bais Shammai more stringent.

If we take this approach we could answer that in Messianic times, we will be living on the highest level; there will be no need for subjective applications of Torah principles. Each halacha will be fulfilled and expressed at its full potential (Bais Shammai) and not require interpretation or application.

Another answer that occurs to me is as follows. The Tosefta (Sotah 13:3) uses the phrase “Until Eliyahu comes” as a figure of speech for an era, and not anticipation of his prophecy:

“This can be likened to a person who says to his fellow, ‘Until the dead are resurrected or until Elijah comes.’” (This is similar to a Gemara Sotah 48b but interestingly omits the phrase “until Eliyahu.”) This is based on interpreting a figure of speech in Ezra (2:63, see Rashi).

Therefore, we can say that “When Eliyahu comes” is not referring to his prophecy but rather to an era. That is, in the Messianic era the level of Torah knowledge will be at such a peak, we anticipate the ability to resolve the halachic questions. Not by prophecy but rather pilpul, as had occurred during the era of Asniel Ben Knaz (Temurah 16a).

This is a plausible answer except that it does not fit well with the actual text of Rashi in our sugya, who says “Eliyahu will answer the question,” unless Rashi meant it also as a figure of speech.