My point is is that if the OP intends to produce a stallion intended for a specific discipline, it is recommended to use blood that produces horses for that intended sport. The goal isn’t to produce a horse that can get over a 3 foot fence with pretty good form - the goal is to produce a prepotent stallion that will consistently produce a certain type. Tall orders. And in general, Europeans do not really focus on producing hunters, but you will find American breeders with stallions known for producing hunters - none that I can think of as a full TB.
My biggest point here is that this will be a very expensive and probably near impossible endeavor. I’m wondering if OP if familiar with the stallion approval process and the cost associated? I am, it is not for the faint of heart. I don’t think I’d ever suggest this approach that the OP is considering - using a breed that is rarely approved for major WB registries (and if they are, they are typically an anomaly for the breed), for a sport with very few TBs established to produce this type. Getting a stallion prospect from the most proven of lineage is challenging. This is a bit like the Wild West. Also, the clientele as you mention is going to be challenging - the sport is largely dominated by WBs, so is it wise for OP to spend 80k to get this stallion approved to have a very limited demand for? Will OP be able to breed enough mares each year to even keep licensing? Lots to consider here.
If this were me, I’d forgo the expense, time and process of WB approval and what’s needed to maintain approval and just aim to produce a nice TB Jockey Club stallion with the intention of producing hunter/jumpers.