Intel began promoting the BTX form factor PCs in the second half of 2004 and hoped that increased digital home applications would help push sales, and that the segment would account for 15% of global desktop shipments by the end of this year, the sources noted. Intel also projected that BTX PCs will become the mainstream PC platform in 2006, replacing the ATX form factor.Read more at DigiTimes
However, BTX motherboards will account for only about 5% of global shipments by the end of this year, well behind Intel’s expectations, the sources estimated.
This year won't be the year of BTX

Taiwanese motherboard makers say that BTX motherboards will reach the sales channel in the second quarter of this year, but that BTX won't become mainstream this year.