I have no good idea. Sorry.
I wrote a PM to some guys who participated in CHM or participate in the new project and should be more familar but no response yet (a guy from Spain, a guy from Italy and an "international expert"; they are used to complain/discuss about the numbering mess).
Well, in general, I'd like to map all European motorway-like or expressway-like routes. Many of them are signed like simple 2-laned main roads, so I'm not sure if all roads of this category should be mapped (a lot of stuff to keep it up-to-date).
All Danish PR roads which have motorway standard (e.g. PR18, PR15,...), Swedisch roads which have motorway standard (e.g. 40 east of Gothenburg), German "Yellow Autobahns" (B roads like B2, B6, B10, B14, B15n, B17, B27, B29, B30, B49, B50, B243,...), Croatian D expressways, Dutch N expressways,... Just look at
my damn list of u/c projects from this category 
.
But if I got you right earlier this year, you don't want to add sections depending on the technical standard but depending on the road category, e.g. not only German "Yellow Autobahns" but all B roads.