AGeese
Crowing
I was going to say and then read your last paragraph, Horner isn't reproducing any particular dino, just funnin' for science.Actually, not so much: we don't have any genomic data from terror birds, and we also don't have a convenient source of eggs in which to gestate them. (Even the extant ratites we do have, like ostrich and emus, are quite distant relatives and can't necessarily be expected to provide a suitable developmental environment for a terror bird in the egg--maternal egg yolk provisioning can vary quite substantially among species! The closest living relative is probably seriemas, which are much smaller than any terror bird species.)
If you were going to try and de-extinct a large terrestrial bird, your best bet is probably moa, but even that is going to be considerably harder than playing with various developmental gene expression factors to try and re-engineer teeth out of a beak or encourage distal claw growth on wings. We are not anywhere near successful "de-extinction" of any species, even those we have complete (or complete-ish) ancient genomes from.
On the scientific end of things, the draw is mostly using the "cool factor" of the project to justify funds to learn more about gene expression during development and how transcription factor expression and gene regulation can contribute to complex phenotypes. It's all developmental genetics. You're not going to learn much about dinosaurs qua dinosaurs from the project: as far as evolutionary biologists are concerned, any chicken is a perfectly representative dinosaur already just as it is.
We could start with Seriema and breed for size, there's another decendant species too, but I forget. Maybe the Secretary Bird?
Speaking of ground hawks, have you seen the Northern Crested Caracara? It's actually a Falcon that likes to spend a lot of time on the ground and really has that look.