there are NO such things as "modern traditional songs"! This is a category error. There are songs that do sorta well following the style of some old songs and 'feel' traditional. And some of these may gain traditional status in 40-50 years.

Just using the phrase "traditional music" indicates that you think you will recognize it when you hear it...so...if a new song doesn't fit the template, it is just a new song...maybe a good one, but NEW!

If you look at 10,000 songs and examine what it is in them that makes some feel like 'folk' or 'trad',(tune style, subject matter, lack of commercial format, anonymous author, etc.), you will have a general list to judge new songs by...it won't tell you which are "good", but it will tell you which bin they belong in at the store.