I used to use this (still do really) as a technique when starting undergraduate lectures. They’re there, ready to listen, but chatting away and need a moment to focus their attention. *SO* let me tell you further fun facts about carbonyl chemistry… Works. Those Anglo-Saxons knew what they were about.
I'm confused, isn't this the exact usage that TFA is refuting? > Yet for more than two centuries “hwæt” has been misrepresented as an attention-grabbing latter-day “yo!” designed to capture the interest of its intended Anglo-Saxon audience urging them to sit down and listen up to the exploits of the heroic monster-slayer Beowulf.
Heaney's famous translation begins "So. The Spear-Danes ..." with that "So" being an interjection, a thing that could in principle stand on its own. (You might say "So." and wait for everyone to settle down and start listening.) Even more so with things like "Yo!" or "What ho!" or "Bro!" or "Lo!". (Curious how all the options seem to end in -o.)
This is more like "So, the Spear-Danes ..." where the initial "So" has roughly the same purpose of rhetorical throat-clearing and attention-getting, but now it's part of the sentence, as if it had been "As it turns out, the Spear-Danes ..." or "You might have heard that the Spear-Danes ...".
I think the theory described in OP makes the function of "hwaet" a little different, though; not so much throat-clearing and attracting attention, as marking the sentence as exclamatory. A little like the "¡" that _begins_ an exclamation in Spanish.
Of course a word can have more than one purpose, and it could be e.g. that "hwaet" marks a sentence as exclamatory and was chosen here because it functions as a way of drawing attention.