thank you! I think a faction with Germanic and Celtic elite units representing the rulling class and Baltic, Finnic, Proto-Slav, Sarmatian and Dacian Recruitable Other Units would Rock!
Germanic Elite Units: Cimbri, Ambrones, Teutones, Marcomanni, Belgae, Bastarnae?
Celtic Elite Units: Boii, Taurisci, Scordisci?
Maybe with the possibility of choosing Eastern Celtic path or Germanic Path... if not Celtic tribes should be RoR alongside Lugii, Venedi and other lesser Germanic tribes...
RoR and/or AoR: Venedi, Lugii, Rugii, Guthones, Quadi, Costobocii, Iazyges, Alani, Roxolani, Cotini, Scythians, Serdi, Pannoni, Veneti, Autariatae, Triballoi, Helvetti and other Western Celts and Celtiberians perhaps...
Edit: knowing that at first the rulling class of Northern populations was indeed of Celtic origin in majority but then was slowly replaced by German and Sarmatian nobles like Cimbri, Ambrones, Teutones, Belgae, Bastarnae and Marcomanni maybe a Germanic faction with the upper tribes as elite units and Baltic, Finnic, Dacian, Celtic and Lesser Germanic tribes as bulk is the best option. Nonetheless I strongly encourage the possibility of recruiting Elite Eastern Celtic, Sarmatian and maybe Dacian and Proto-Slav (Przeworsk) as Mercenaries/Allies to show the diversity and ever changing situation of that region!
It was hard for me to decide between choosing Cimbri, Ambrones and Teutones instead of Taurisci, Scordisci and Boii but... I think it's the better choice... Of course the possibility of allowing the Western Celts to hold regions in Bohemia, Noricum, Pannonia and perhaps Tylis and Galatia, for a better gameplay even if it will be a somewhat artificial state, still exists!
another question is were Northern Dacians subjects of the Bastarnae or were Bastarnae subjugated by Dacians/Sarmatians! And what about Cotini!? Were they subjugated by Bastarnae and later Sarmatians?
well knowing that a very large army of Bastarnae migrated south to help the Macedonians against the Dardanians on their free will what do you think? I think they chose to fight alongside Macedonians and then be part of an alliance of Dacians, Sarmatians and of course Bastarnae! but indeed after a while they were Sarmatisized! if the word even exists!
oh and what about the Illyrian and Thracian subjects of the Scordisci and Taurisci? where will they be included? oups... maybe AoR... my head hurts! or maybe they were already integrated!? well those from the Alps sure but no way those from the Balkans! they riot today still!