It wasn't your comment on Rylais, it was your comment regarding Iceborn.
I spent my entire time on that post stating that you shouldn't build AP Leona for pure bursting and that was why I mostly disapproved of it; I saw the AP as more a nice little bonus to add on to the disruption and lockdowns. Building a rabadons wouldn't really profit in the long term because the damage contribution would end up pretty small.
I'd probably end up taking AP items that either contribute to your bulkiness or to the team; Abyssal Scepter, Rod of Ages, the like. Building pure AP on Leona is going to get you absolutely nowhere, and the problem with her is that she can't deal high damage. Simple as. Ultimately, she's going to end up making the rest of the team become carry as fuck anyway. I just think AP is a different way around of doing it compared to normal Leona. Sorry if I didn't make that clear in my previous post.
I suppose it does deviate from the idea of putting her in mid lane, but I'm just referring to her building AP in general now.
Also, does your formula for the AP Leona damage put in Lich Bane in any way? Because I'm pretty sure it'd be a good contributer to her Q, and in lategame she'd generally be able to pull off more than one Q in a teamfight while sticking to a target. I get your idea, though, and I can see why Leona can work as an AD bruiser.