You mean the St. Regis Bangkok dynamically offers different SNA upgrade options online based on the room already on the reservation? Or that's just what happens behind the scenes in practice? I seem to remember someone posting that this hotel has a pretty gauche upgrade upsell menu that they proactively try to push to guests when checking in so anything's possible. (This upsell attempt only happened to me once at the W Seminyak and I hated the experience, finding it downmarket and tawdry and not a little embarrassing for my travelling companion.)

I guess we'd have to ask iknowthings if the current SNA process enables hotels to create multiple SNA pools that are offered to guests with reservations in different specific room categories.

Maybe you're right and the IT does currently enable hotels to do this. It's rarely seen though as I'd imagine (a) the management overhead would be pretty tedious; and (b) most Bomvoy members looking for a suite upgrade with an SNA or at check-in will book the basic room category and hope for the best rather than pay more upfront to book a specific suite and hope for a category upgrade from that.