Since you're trying to keep the campaign in Thay itself right now, I doubt you'd be interested in this, but you could perhaps work some of it in.
Right before TSR stopped supporting Spelljammer, the Thayans appeared to be on the cusp of a truly remarkable breakthrough: they were the first humanoid race to produce a working spelljamming (flying ship) helm (power source) of their own, rather than buying one from the Arcane (blue-skinned giants, basically the 'mercane' of the Epic Level Handbook). This would have been a world-changing event for the Spelljammer setting, propelling Thay far ahead of its neighbors in the fantasy space race, into an entirely different league of powers. At least, that's how the Thayans saw it...
Perhaps your PCs could be involved in some way with the development of the so-called "Grand Helm" of Thay. All of the Thayans' neighbors and rivals, particularly Waterdeep (the other major spelljamming 'Western' power in Realmspace), would be desperate to either steal or destroy the plans before such a device could be built.
Even if you didn't use Spelljammer material, the idea of the Thayans, with their masterful magic item creators, being on the cusp of a major magical development that other nations wanted to destroy would be very interesting. I'm always fond of 'defensive' scenarios to break up the usual pattern of most campaigns, forcing the PCs to protect their stuff and themselves from folks who want to kill them and take it.
Of course, this being Thay,
somebody is probably backstabbing somebody else. What's selling the plans for the Grand Helm to Waterdeep compared to the chance to humiliate a rival Red Wizard?
Option one: the PCs are affiliated with the faction working on the Grand Helm (or its equivalent), in which case a higher-ranking Red Wizard might recruit Kesia as one of the testers for it (spelljamming helms drew power from spellcasters who sat in their throne-like contraptions) and the others would have to protect her from an assassin or kidnapper while she attempted to control it.
Option two: the PCs are involved with an opposing faction, and called in to disrupt the 'dangerous experiment' of a 'tragically - terminally - misguided' Red Wizard. But, they have the opportunity to discover that the Red Wizard who gave them the task is actually conspiring with filthy Waterdeepian scum (or Shou Lung scum, for a more globe-trotting, Kara-Tur twist)! Now they have a choice between betraying that wizard or possibly betraying Thay; of course, they could always blackmail him, to...
Unfortunately, I know a fair bit about Thay from using it in Spelljammer campaigns, but next to nothing about the rest of the Realms, so that's all I've got.