There are any number of things I would like to see, any of the previously mentioned items are great. Since there are a lot of new AR owners out there right now maybe there needs to be 2 or 3 segments or more. A lot of non tactical sportsmen and shooters have recently acquired their first AR. I know many who have, that had never had an interest in them before but do now because of the current political climate. Because of so many new AR owners I think a basic run down on theroy and operation on ARs would be great starting with the basic basics and advancing from there. Actually you could probably make a series out ARs alone.
2nd would be general cleaning and maintenance, what and how to lube etc. Spare parts, what to watch for in terms of ware, pitfalls when maintaining and replacing parts, etc.
3rd, Slings. Seems like there are a million differant types of slings, attachment points, and gizmos to attach them with and ways to use them. I can't tell you how many times I've read something about using x sling with a z setup and I have no idea what there talking about because they assume everyone knows about it already.
4th, ammo, what ammo for what, bullet weights and types for the different twist. Maybe an overview of .223 vs 5.56 and throw in the .223 Wylde and any other specialty chambers.