BT is dying if you ask me. Classic BT anyway.
The "death" of BT has nothing to do with the removal of the Unseens. And, btw, the Unseens were never portrayed as the "crappiest" of mechs. Many of them were quite capable, like the Warhammer/Tomahawk, Marauder/Gulag, and others. Only the LAMs (Land Air Mechs, BTizations of the GERWALKS) and the mech representations of the Valkyries as a whole had any suckage (IMO)... However, the Shadowhawk (IIRC) which was the BTization of the Super VF-1S Battroid (IIRC) was the official mech of the Steiners (IIRC)... Not too shabby.
The Clans used many "unseen" designs and used them quite extensively even if they were "Second Line" mechs.
BTW, WizKids has redesigned the "Unseens" and is now re-releasing them in a George Lucas-esq rewrite of Battletech History (though I don't think they're re-writing history, I believe the official word is that the redesignes are new updated versions of the same old classic 'mechs.)
Vostok 7