I'd be glad to receive feedback. I'm starting to like Don's thinking here. XML has got some historical baggage. If it were really SML 2.0, SML 1.0 would have had the same baggage. But it seems that the baggage is what people want to eliminate.
Entities are an example.
That would probably simplify things. But then you aren't a subset of XML anymore. On the other hand, if you omit DTDs, you could still be a subset. Look at the number of arguments about attributes that are being posted. The people who actually write parsers have been saying that there is virtually no cost in memory or complexity to having attributes.