Practical as in what? To increase mpg or to decrease emissions, for a certain cost?
I'll wager a "nope" regardless. If it could do either, it likely would have been done already. OEM's have a lot pressure to meet certain targets.
for a passenger car. No. Crankcase windage loss at 2000 RPM is quite small. At 8000 it is significant. Plus race engine are a little loose, and have very thin low tension rings, so can benefit from crankcase vacuum.
Your car already has a huge vacuum pump, the engine itself. You don't want or need additional positive or negative pressure (a vacuum) in a street engine as either can cause seal failure.
Some engines like diesels, forced induction and those with big cams require an additional pump for proper operation of the pcv system, brake booster and any vacuum operated controls like those in older cars eg climate control systems, vacuum locks, etc.
No idea what engine you have. On a "classic" engine a slight depression on the internal of a wet sump engine is a good thing as long as no liquid ingested.
It would have to be a large volume pump to exceed what is available from inlet manifold though.
Not to remove fluids but to reduce crank case pressure - would this be practical for a passenger car?
It is done all the time in engines with dry sump systems.
The oil scavenges pumps (plural) pull more oil out of the sump than the oil pressure pump can push into the engine.
There is a partial vacuum in the block, which also means they typically do not need a PCV valve and simply vent the gas off the deaerator in the dry sump into the intakes.
My Ferrari F355 has such a system.