I really like Radja, but I see some issues to be solved during summer and I don't know if he is the right answer. First of all, Matic is not making the cut this season for me, but he contributes with some things that Nainggolan could'nt bring to the club: 1.94m vs 1.75m. The PL style relies on aerial balls and being as tall as Moses is not enough if your partner is Kanté (1.69m). On the other hand, Radja has scored 9 goals and 3 assists vs none and 6 from matic which is quite impressive, but let's face this: we need to do something with cesc and pedro in that case. I would love to see a Hazard-Kanté-Nainggolan-Fàbregas (1.75 again), but that for me means more ball control which is not the team's style this season.
By the way, I think he could get used easily to the system and the "Italian mentality".