Simples Assim

However, it doesn’t seem likely that log4j 1.3 will ever been sufficiently compatible with log4j 1.2 to recommend it as a general replacement for log4j 1.2.

Oh, really?

[log4j 2.0] would include a facade that emulates the log4j 1.3 API but would not be compatible with user written appenders and other components.

What do the dogged open-source advocates have to say?

http://logging.apache.org/log4j/docs/plan.html