As new developments are announced for the latest edition of Dungeons & Dragons, there is a seemingly inevitable litany of complaints.
This time, it's about the announcement that the modularity of the ruleset would allow players at the same table to use different character sheets and maybe even different rules. The more I think on it, though, the more I realize that it's not a terrible idea.
Let's say that the Basic Set for D&D 5e includes the basic combat system (truly the core of any version of D&D), basic classes, and a basic skill system (maybe only a few dungeon-specific skills that advance automatically by level, as in 4e).
Then the Advanced Set introduces feats for each class (Basic Set might have only included a few feats, or gone back to something like Weapon Proficiencies and thus feats are a supplement, not necessarily a replacement, for that), maybe some more classes built around ideas in the advanced combat rules, and the skill advancement is broken down into 3e-ish skill points for finer customization.
There's really nothing keeping an Advanced Character and a Basic character from sitting side by side. The Basic character may be proficient in 5 weapons and have a static value in their skills, while the Advanced character has spent his 5 proficiency slots being that much better with his longsword (maybe picking up a few tricks) and might have fewer points in each skill, but have points in more skills.
The only real challenge here seems to be the implementation of prestige classes (or whatever they decide to call them). For much of their existence, prestige classes bribed players to take them by offering significant power boosts when compared to a base-class character. But since Basic (no p-class) and Advanced (p-class allowed) characters would have to balance against each other, this sort of thing really can't happen.
There even seems to be hints of a 3rd set for activities "beyond the dungeon." with rules for social influence and kingdom building a la Birthright.
The real sticking point here (and I think it's valid as well) is that the pitch they have provided seems geared towards letting players decide the complexity of the rules used at the table, instead of the Dungeon Master. And since the DM is the one making the rulings on the events at the table, I think letting them make the decision as to what rules are going to be used in those rulings is perfectly fair.