A point occurred to me as I was reading the analysis of this abrogation claim. The preposition used in 2:284 is "ب" not "على" as the verse says "يحاسبكم به الله" not "يحاسبكم عليه الله".
It occurred to me this morning to ask, "why is it that everybody interpreted this verse negatively? i.e., why didn't anybody ask what happens to us if we think good thoughts
?" The answer came quickly, by noticing the subsequent sentence, "so, He forgives whomever He wills and torments whomever He wills." So, the context is indeed about bad thoughts. God forgives those who do not turn them into action, but torments those who do. That is the accounting God talks about in 2:284.
That said, the question itself merits an answer. And the Prophet, peace be upon him, gave the answer when he said, "Whoever is about to make a good deed but doesn't, it is written for him as a good deed, and whoever is about to sin but doesn't, it is written for him as a good deed!" Thus, God counts for us our good thoughts as good deeds, and stopping short of sin as a good deed also! Thank God for His Grace. It stands to reason, therefore, to conclude that only bad thoughts that materialize are the ones that are accountable as sins.