kernel impar y opcion en desarrollo

El segundo numero se refiere a un kernel en desarollo y que no se considera estable todo el :P
Lo que tu dices es una opcion para compilar en el kernel drivers que no compilan limpliamente o que son experimentales pero estan dentro de un kernel estable, en la propia config del kernel puedes leer:

Some of the various things that Linux supports (such as network
drivers, file systems, network protocols, etc.) can be in a state
of development where the functionality, stability, or the level of
testing is not yet high enough for general use. This is usually
known as the "alpha-test" phase among developers. If a feature is
currently in alpha-test, then the developers usually discourage
uninformed widespread use of this feature by the general public to
avoid "Why doesn't this work?" type mail messages. However, active
testing and use of these systems is welcomed. Just be aware that it
may not meet the normal level of reliability or it may fail to work
in some special cases.