I've got blueberries in ground and some in pots (waiting for space in the ground) and the ones in ground are so much more productive.

How are you going to manage pH?

You will likely have drainage issues, and due to their roots, they do like good drainage.

What kind/amount of tree roots are you talking about?

Also, buying pots seems expensive. Plus you have to dig a big hole for them. You would dig a smaller hole for just the plant.

The pot looks better than the container from WalMart. You might also look into fabric pots. When the sun hits the container it will become brittle in a year or two. Pots tend to last much longer. Even 5 gallon buckets will last 4 or 5 years without getting brittle.

Putting the container in the ground will cause drainage problems. The only area for the pot to drain would be through the holes. They could get clogged and nothing would drain out. You could put in a raised bed and fill it with acidic material. Over time the bicarbonates from below would move up so you would have to balance that with sulfur and acidic fertilizer.

The spacing could be closer with potted plants. Where I am located the plants tend to be the diameter of the container they are in. You can control the height by pruning.

I think that the only way that your idea of putting your containers in the soil would work would be to dig a hole for a 5 gallon bucket, cut the bottom out of the bucket and use it like a raised bed, but in the ground. As long as you do not have a high water table I think that might work. The roots of the blueberries should fill the buckets, at least they do when left above ground.