"A later revision of IEEE 754 attempted to remedy this, but the formats it recommended were so inefficient that it has not found much acceptance."

IBM put hardware support for the IEEE 754-2008 Decimal Format in their POWER architecture. The POWER7 clocks 5 GHz. Decimal floating point is only considered slow because Intel and ARM do not have any support for decimal floating point in hardware. Lack of acceptance probably comes from lack of support in standard libraries rather than inefficiency inherent in the standard.

Reference: https://en.wikipedia.org/wiki/POWER7