In the article Hebrew Henotheism: Challenging the notion of Biblical Monotheism, the case is made that the Shema was to be understood relationally with Israel.
The 1985 edition of the Jewish Publication Society translation of the TaNaKH portrays this when they translate the verse as “Hear, O Israel! The LORD is our God, the LORD alone.” This reading displays that Yahweh is the only god that Israel is to have, echoing the first command to not have any gods before Yahweh.
The argument is made from a few other passages that the emphasis is not on YHWH being the only true God, but the only God for Israel. The implication is that it does not say other gods do not exist, but only that YHWH is supreme and is to be the only God of Israel.
The article Monotheism, Polytheism, Monolatry, or
Henotheism? Toward an Assessment of Divine
Plurality in the Hebrew Bible briefly comments on the Shema and seems to agree:
Even the Shema and the first commandment do not consign the other gods to fantasy, since the demand is
made that no other gods should be worshipped.
This would not be particularly unacceptable as an opinion built on a framework, but the prior article explicitly claims to be only interpreting it from a literary perspective, absent a theological frame. However, it earlier references the Deutero-Isaiah writer theory and goes on to examine Deut 6:4 alongside Isaiah 44 as though they were contemporary. Some form of documentary hypothesis, a priori, does seem to be at work here.
I would be uncomfortable not adding that several of these arguments are made purely from a literary interpretation that is so literal that it would make a young earth creation Southern Baptist blush. Quoting the 20th century JPS translation while ignoring evidence such as the 3rd century Carnuntum Shema fragment, which translates the echad in a Greek 1 showing a clear numerical declaration (one, not alone), seems irresponsible, as if it is a better representation of the pre-exilic understanding. It may be, but it fails to wrestle with any opposing evidence or translations.
The article also fails to communicate whether it is making the argument that the Shema is intended to be henotheistic or whether the Israelites simply practiced henotheism, a claim the biblical record would largely agree with and then condemn through the prophets. The article seems to blend what the Shema does not explicitly deny (that there are other gods) with what the Israelites practiced (worshipping other gods alongside or instead of YHWH) and come to the conclusion that this suggests a henotheistic meaning for the Shema.
The article also makes several other inconsistent arguments that seem to pick and choose evidence and how and where to interpret and translate passages that best support it. This is beyond the scope of this question of course, but I felt a warning to those reading the article was warranted.
This critic would argue that asking "does the text explicitly deny this?" rather than "what does the text intend to mean? is a poor hermetical approach, regardless of the topic or my feelings on it.
That said, this particular take on a henotheistic Shema is simply choosing to take the position that since it doesn't literally, explicitly demand a monotheistic meaning, it must not be monotheistic. It does not allow for mentions of other gods in Deuteronomy to be abstract references to nonexistent gods that the Gentiles believed in, but rather as references to literal gods that are assumed to exist.