I agree completely that we can interpret this visit and conversation to Darcy "practicing" and sounding Elizabeth out.

Notice also the movement of his chair:

Mr. Darcy drew his chair a little towards her, and said, "You cannot have a right to such very strong local attachment. You cannot have been always at Longbourn."

Elizabeth looked surprised. The gentleman experienced some change of feeling; he drew back his chair, took a newspaper from the table, and, glancing over it, said, in a colder voice...

He moved his chair towards her, creating a more intimate scene, but he drew it back when he experienced a change of feeling. Was that change due to her surprise, or perhaps his own surprise that he has said/done what to him must be an indication of his feelings? (Remember back in chapter 12 "He wisely resolved to be particularly careful that no sign of admiration should now escape him, nothing that could elevate her with the hope of influencing his felicity; sensible that if such an idea had been suggested...) I can't help but think that Darcy is having the same qualms again, and he thinks that by his words and actions in this tête-à-tête he is giving Elizabeth too much informtion, especially if he is not yet decided about her.