I don't think certification is a problem. Both multi-engine and Last Mile Traxxes were sold before they've got any certificates. About Vectron - I think private operators suffer from the crisis, in last year (or two) there were not many orders for brand new locomotives at all.

I just think last mile locos won't be as popular as producers would like them to be. They're not strong enough to operate on non electrified lines, moderately useful for shunting (I think Traxx Last Mile's 240kW isn't much, plus most stations have proper shunting locos), more expensive to buy and operate (inspections/repairs).