The implicit point being that for any "special rules" and encounter balance zots, she'd rather have that dedicated not to the party of 4+, but rather for the party of fewer than 3. Citing sales and her own enjoyment with friends as the main motivator there, and some skepticism that any form of XP scaling could do the trick on its own, particularly at the low end. That's how I read the gist anyway, unless I was way off track. Was that the right read Alyssa_Fox? Is that your thought as well mrfuji3?
To be clear, I'm FOR an allowed party size of 6 (via a dedicated defaults-to-off checkbox in the settings) that uses split exp. Modifying the exp formula could easily balance everything for parties >4.
But I do agree with Alyssa_Fox that split exp might not work that well for 1-person parties, possibly at all levels. At low levels, an increased-exp solo-er simply wouldn't have enough features to resist common enemy CC/shoves/surfaces/damage. At higher levels (with increased exp), a solo-er would reach the level cap and thus sharply drop off in power beyond that. Also, while systems like Pathfinder grant skill points each level and increase ALL STs with higher levels (even AD&D 2e did this, right?), D&D 5e only increases your proficiency with a subset of these. A level 20 5e sorcerer, barring feats/subclass abilities, still only gets their Wis Mod to Wisdom STs.
Honestly, I'm mainly theory-crafting for fun at this point: "given no extra exp, how could one balance a party of 1-2 characters for normal encounters?" It's not like Larian is actually reading this thread. Or if they are, they've likely already come to their conclusions.