What you are asking for is not just a matter of expanding what the search engine looks for.
It involves creating an entire new array to be filled in by the tree-indexing software.
This can be rather taxing for software since in the millions of trees there can be myriad variations (individual to individual) on how many events are entered and of what type.
I have some individuals with dozens of military and tax-list entries, some with dozens of residences generated by city directories, many with burial data, many without.
Think of creating a single spreadsheet for just the persons in your tree, with a column dedicated to each instance of such facts as the above. Multiply that by (say) a hundred million, and you get an idea of what sort of server-resources that entails.