Unless Ds make serious gains in AZ & GA in 2018 I don't see the benefit in adopting that strategy in 2020. Ds were winning in VA/CO downballot before they starting seriously targeting the states while they haven't won in AZ & GA since 2006.
They literally only started winning major races in off-years in VA and CO (asode from Salazar who was a popular AG) in 2006 before they won there in 2008. GA and AZ can very much swing as much as those states did in 4 years
Yes, I'm saying we should watch how 2018 goes before going all in. There's a Senate race in AZ that should be a target and an open Gov race in GA and plenty of row offices as well. Our chances in MI, PA, WI in 2018 alone are a lot better in AZ/GA right now.