Right—that's the power and beauty of a good metaprogramming system is you can extend the language to meet your domain—not the other way around. Type tailoring is all about (ab)using metaprogramming to target the elaboration of surface syntax into something the type checker understands. So, the reason why it's sounding familiar is because type tailoring uses metaprogramming and targets eDSLs. Some of the stuff you're likely referring to (please send me a link with examples) probably is doing type tailoring.
The problem is that, until now, there hasn't been much awareness of the underlying thing going on here with types and metaprogramming. You might implement an eDSL with macros and get some nice type checking for free (I'm working on another project right now that does exactly this) but, with this type tailoring framework we're proposing, you might see ways that you can get more out of what you're doing by leveraging static information better and by programming the elaborator more cleverly. Does that help?
The problem is that, until now, there hasn't been much awareness of the underlying thing going on here with types and metaprogramming. You might implement an eDSL with macros and get some nice type checking for free (I'm working on another project right now that does exactly this) but, with this type tailoring framework we're proposing, you might see ways that you can get more out of what you're doing by leveraging static information better and by programming the elaborator more cleverly. Does that help?