Yes, anything marked deprecated should almost surely be removed.

Re; filtering, I'm not sure what you are asking. I suppose that having a filtering api is an OK idea, even though there are few users.  I suppose that having some pre-defined filter predicates is an OK idea, so maybe  STIAboveThreshold could stick around.

How to 'combine filters' is a trickier question. I googled that a few months ago, found answers on stack-exchange, which seemed to be that "combining filters is not supported in c++11, but you can use these wild-n-crazy BOOST stunts to do the same thing and someone really should put it in the c++14 standard..." and it seemed to me that dicking with boost to create something that no one is going to use anytime soon was maybe a poor idea ...