Hi Woland,
We are currently looking at allowing some customization of the history table mapping but it's not yet clear what level of customization will be provided out-of-the-box. It seems unlikely that the level of changes you are suggesting would be part of this.
However, we are also moving to a model where more of the services of EF are abstracted out and can then be replaced by different implementations. (Take a look at IDbDependencyResolver and the services it currently resolves for examples.) We are definitely interested in the kind of contribution where you can come up with appropriate abstractions for the services for which you then make our implementations the default while allowing them to be replaced by whatever you want.
Along the same lines, if there are smaller changes that can be made to DbMigrator that would allow it to be extended to do what you want then we might also be interested in that.
I guess the bottom line is that we would generally love contributions that make EF more extensible (as long as its done in a nice, clean way) because that opens features up for different less common scenarios without taking all the changes required for the less common scenarios directly into the core.
Thanks,
Arthur