std::shared_ptr provides a limited amount of type erasure natively
based on void* and the fact that it stores the original type in the
deleter. As a result, if you know the original type, you can call
std::static_pointer_cast and recover a legitimate shared_ptr of the
right type, very efficiently.

It looks like the use of boost::any in this code is:

1) to hide the pointed-to type so a uniform container can be used
2) to represent "no pointer"

both of which can be handled natively by shared_ptr<void> with a small
performance gain from removing one indirection.