I am not aware of anyone using the U-Boot API for grub these days, so I'm not sure it's an incredibly useful goal. The main pain point distros seem to have is to make something that "just works" on all systems out there. Moving into that direction should be our ultimate goal.
Please note that with the generic distro framework U-Boot will grok https://wiki.freedesktop.org/www/Specifications/BootLoaderSpec/ and things Just Work. I setup a bunch of SD cards with Debian and Fedora over holiday so I can drop them in whatever board and boot up Linux as a sanity test.
This is certtainly Fedora's preferred method for u-boot based devices
I certainly can see a usecase for kicking off an EFI binary as part of fitting into existing work-flows. But we do already have a something for getting rid of that particular pain-point and it's working :)
It would certainly be a useful option to have.