Du Pont Bulk Powder was made, and available, into the 1950s to early 1960s, when it was finally phased out.
It was intended for use in shotshells and SOME rifles with modern steel barrels, NEVER in muzzleloaders.
Du Pont over the years also had a number of other bulk replacement powders, each of which was adapted to a different class of arm.
Schuetzen Smokeless was adapted for rounds like the .32-40 and .38-55 using lead bullets.
Empire was another intended primarily for shotshell use, but apparently wasn't popular and was phased out after a relatively short life.
Sporting Rifle 81 was adapted for loading black powder military cartridges up to, I THINK, jacketed small caliber rounds.
Other companies, like W&A, Laughlin & Rand, and later Hercules also made bulk replacement powders for a time.
I THINK that Laughlin & Rand may have been the only company to make a powder that suitable for use in iron-barreled muzzleloaders.
"Can't we consider Blackhorn 209 as a modern "bulk smokeless" powder?"
No.
It can't, to the best of my knowledge, be used as a bulk for bulk replacement for black powder.
Probably the closest thing we have today to a true bulk replacement powder is Trail Boss, but it does its work at relatively high pressures. So even it is not a candidate for use in some of the arms that a true bulk replacement smokeless would be used for.
"Neat stuff, which I felt should be considered "semi-smokeless"."
Semi-smokeless was always kind of a nebulous term that could be applied to black powder-type formulations using modified materials (Du Pont Brown, Prismatic, or Cocoa powder [all names for the same product, and used primarily as a military propellant for land artillery and naval use) or also for nitrocellulose formulas designed as bulk replacements.
Traditionally, PB was never considered to be a bulk replacement nor semi-smokeless.