MyTokens support would allow for the creation of some awesome dynamic scripts without having to jump through major programming hoops to get things to work semi-dynamic. For example, creating Promotions for coupon code that work on only a select number of products. Since you can't query the database from the XLT script, the only way is to hard-code all the product variant id's that are eligible for discount in a very long IF statement block, or a long delimited string to be used in a compare function.
MyTokens would give the ability to query the database directly, pulling out all the Variant ID's for a specified criteria (ie: Product Name). Then the XLT code can be written in a more generic way, so that should the database items change, no need to change the XLT as well. It would allow for less manual maintenance, and having to remember all the areas that need to be maintained on changes.