C# – Pattern for multiple datasources

You should look into Spring4D as it already contains nullable types (similar implementation as yours with a little extra operator overloading) and way more powerful collection types than those in the RTL. They are also interfaced based which is very handy because you don't have to worry about lifetime management especially when passing them around.

For cross referencing problems I am suggesting coding against interfaces and use these as reference in another implementation rather than 2 implementations knowing each other.

As for the MVVM part you might look into DSharp which has a first version of a Caliburn Micro port for Delphi. It is very early stage and hardly documented but you might get some ideas how to achieve MVVM in Delphi using loosely coupled GUI and business logic connected with data bindings. The Blaise Pascal magazine had two articles about it if you are more interested.

P.S. I guess you mean you are using XE6 as that is the latest version.

I oppose to use macros instead of normal class here because:

1. It is harder to debug, especially when it has compile error

2. If the cost of creating a new class easily is harder to maintain later, I prefer do more works to create a class but easier to maintain later

3. I believe a gold of quote would be applied in this case :"Reading code usually cost more time than writing code"