Bismihi ta'ala
There is no shar'i problem at all with a Seyid/Seyidah marrying a non-Seyid/non-Seyidah.
Islam encourages married based on the criteria of Din and Akhlaq. Please review Ayatullah al-Udhma Seyid al-Sistani's advice to the youth, where he mentions this as well:
https://www.sistani.org/english/archive/25240/
Wassalam