Depending on conditions and soil types, it can be very challenging to get a uniform depth core, especially on clay or compacted soils, and our dry sandy soils.  There are some pretty slick auger/drill machines already marketed.  The biggest weakness I see in them is in the collection bucket, as they are are usaually a little weak and brittle, and hard to dump.  

Some run off hydraulics powered by an auxiliary gas engine, others off a 12V drill motor run off the ATV battery.  I am not sure which is best.  I saw a man in Alabama with a Dewalt 18V drill running his, said he liked the extra power he got from the 18 volts, and he must, because he had about six extra batteries in a storage basket. 

Using a conventional probe, I like to pull about three to four samples a trip before emptying buckets to bags, speeding things up a lot when grid sampling.  Another advantage to that system in wet conditions is dirt dries out a little while pulling the next buckets.  I don't see any way to do that with any of the auger/drill sytems out there.

I've seen rusty probes and buckets skew zinc results high, so you have to be careful of material choices.