BTX went the way of Dodo.
Maybe not.
But anyway, BTX was not really meant for high end systems from what I recall, its more for the basic office system. Given that its the gamers/enthusiasts that more or less dictate what stays and what doesn't, BTX was doomed when they announced it....
It wasn't a bad form factor tho, its just that we enthusiasts prefer to have cold air running through everything, instead of having warm air being sucked through the CPU, then through the PSU, etc, etc. We'd rather just get a couple more fans, which was what BTX was trying to acheive: less fans.
It might still stick around, and with a few mods, it might just make it.
RDRAM failed cos of different reasons, it was a good try I'd say with that too, just that Intel couldn't keep its promises of higher capacity. Not in time at least.
Dual Channel DDR RAM killed it a few months later.