As it stands, there’s only 6 non-English teams mooted to be involved. There’s still absolutely loads of quality European teams who would still be involved in the “normal” UEFA comps. Plenty of whom have long standing pedigree and history.
I’m sure if this break away did happen (which I very much doubt will), the CL and EL would still continue with teams including those below, and the fixtures would offer much more variety and would definitely be much more interesting
Bayern Munich
Dortmund
Leipzig
Wolfsburg
Sevilla
Bilbao
Villarreal
PSG
Lille
Monaco
Atalanta
Napoli
Roma
Lazio
Ajax
PSV
Feyenoord
AZ
Porto
Sporting
Benfica
Anderlecht
Brugge
Antwerp
Besiktas
Fenerbahce
Galatasaray
Salzburg
Rapid Vienna
Olympiakos
Panathinaikos
AEK Athens
Celtic
Rangers
Young Boys
Basel
Lokomotiv
Zenit St Petersburg
CSKA Moscow
Spartak
Scandinavian teams
Eastern bloc teams