From a story construction standpoint, I'm inclined to think the content of that letter will be an end-of-Season 2 cliffhanger at this point and lead to a new character arc in Season 3.
Ye old "hero's" journey arc:
Season 1: MC is bottom of the pile just doing as he is told. Doing pranks and getting into trouble.
This phase has ended, as emphasised in several scenes, the most important marker being the talk with Derek:
Immediately following which, the MC decides to be step up and be a problem solver and heads to Cathy, resulting in the look of incredulity on the faces of Bella and Jill seeing a new facet of the former maggot.
Season 2: MC Steps up as more of a leader and is
seen by others as problem solver on campus - and not just by the DIKs
The transition to this phase of the "Hero's Journey" was also marked by several scenes; some obvious such as the speech on the DIK stairs, Sage's comments etc. plus, importantly;
There's a lot of Season 2 left to go before the letter potentially triggers the next stage in the "Hero's journey" methinks.
Season 3: MC is potentially rich? Comes to a fork in the road between integrity and social climbing? We'll see.