Total personal opinion follows: Many years ago I read that business avoided SGML/XML for a variety of reasons, not the least of which was complexity vs. benefit. The same article said that after some time, those that worked with a structured language became enthusiastic advocates. I read the article because I was forced (another reason it's avoided) to deal with data that was in SGML format and I was trying to figure out how to publish printed material with it so I was trying to understand it. After some years of dealing with the SGML source, it became XML that I was forced to deal with. To this day I still wouldn't call myself anywhere near an expert but I'm enough of an SGML/XML "hack" that I can deal with it, and I'm now an ML zealot. There is only one reason I can see NOT to use XML, and that's because there are not any software apps or utilities related to genealogy/family history that benefit large user groups in their daily activity. Meanwhile imo, it's a shame because since people continue to manually add, edit, verify, and otherwise add value (or reduce it!) to genealogy/family history data in their daily activities, a lot of duplication of effort exists. Since XML is an extensible format, data and applications that use it keep getting better and easier. Imo if software did nothing more than become XML-compliant in reading (any) schema, and wrote to a schema that duplicated GEDCOM 5.5 we would be on the road to a good solution for a HUGE number of people in a variety of genealogy/family history efforts.