The 50th anniversary in 2024 is important. I expect that Wizards will do something special for it, and that it will be a 5e product.
By that time, I would like a kind of rules encyclopedia, that consolidates all the rules that we have so far. Some people will call this 5.5 because there will be noticeable changes in format. For example, choosing +2/+1 will be part of ability score generation and not part of race. Likewise choosing an alignment will be part Ideals/Flaws and not part of race. The word "race" might not appear, with ancestry or lineage appearing instead. But really, all of this is cosmetic, incremental, and more like 5.1 than 5.5.