Can you explain why you want to migrate to Struct over Data?
First of all, I would like to separate the aggregation data and content. This way, I can keep content on GitHub for backup and editing in a different environment than DokuWiki. Secondly, it seems development on the Data plugin is stagnating, whereas Struct is very actively developed. So I guess we will see new features mainly on the Struct plugin.
However, working on 10,000 files in a text editor is a breeze, as I can just search and replace as I like. But I'm all up for learning SQL queries, if and when the pro's of Struct outweighs the con's. Exporting and importing via csv is of course an option. Still, the Data plugin is relatively easy to get into, so you could first check if that one fulfils your needs.
Preferably, if DokuWiki could parse multiple files as part of the page, then my issue could be solved in another way. I have been thinking about this not just for data entries, but also for meta, keywords, description, etc. that are part of the page, though hidden from visitors. So eg. mypage.txt and mypage.dat in the same folder would be parsed as one page, but could have different editing rights.
However, I'm going off topic here, but if any of the DW developers read this, it would be interesting to hear if you have any thoughts on the matter, or if the idea is not very good, or even if there are some existing solutions for my use case, if I made it clear enough.