The Jazayerchis and the Line Infantry are quite similar units, available around the same technologies.

They are however not exactly the same, the Persians EU 

1. has one less strength,
2. a bonus while attacking,
3. one more range,
4. is more costly,
5. requires one less population

so players might want to use them more than the LI.

Sadly, there's no upgrade path toward them but only leading to the LI.

I'd suggest making it a choice.