here is the reasoning on why I guessed the 143gr ELD-X
1) Weatherby has been using Hornady bullets for many years in their ammo
2) Weatherby has recently offered the ELD-X bullets in their 257, 300, and 30-378 ammo
3) 6.5-300 weatherby is the only caliber that they offer berger and swift bullets, all the other calibers have either norma(spitzer) Hornady, Nosler, or Barnes Bullets. So from a company point of view, it don't make sense sourcing bullets from berger and swift just for one caliber, when there is just as good of bullets available, from the bullets makers you get the bullets from, for all your other calibers. I could easily see them replacing the 140 gr berger load with the 143 gr ELD-X, and the 140 gr A-frame load with the 140 gr Accubond, and dumping the 130 gr load.
Then again, the 100gr TTSX would be a laser
I guess we will have to wait and see.
Rob