Hi, I believe that "Christian Arabia" cannot be a goal in itself. Arabia (peninsular) had been a backwater since the beginning of time and it is therefore unlikely that anyone would be interested in conquering the most hostile desert known to man just for the fun of it. Arabia before oil has really nothing to offer ...
However, Arabia can remain Christian (it was a majority Christian area by the time of the Arab conquest, albeit not necessarily orthodox Christian) and Christianity can develop deeper roots there as a byproduct of a PoD occurring elsewhere in the Middle East.
While Arabia certainly is peripheral to the Roman and Iranian worlds, I'm not sure that southern Arabia and modern day Oman really have nothing to offer - at the very least a lot of trade flowed through the region. Certainly nobody will be conquering the interior, but the question is more a question of what the best way to make and keep the majority of the Arabian population Christian.
I'm not convinced we ever reached a majority Christian Arabia in OTL. Christianity was common, sure, and well known, but indigenous pagan traditions were as well, and I'm not sure how deep penetration of the Christian religion was pre-Islam. Large Jewish and pagan populations likely existed in many regions, especially in the south, and Christianity's roots in the region seem pretty weak. Indigenous monotheism was also not unknown.
My timeline might not be the best example, as in my timeline Arabia is split between Jews, Buddhists, Christians, and a cult that blends Christianity, paganism, and Buddhism into a heretical melting pot of madness.
P.S. Welcome back f11222, I missed both your timeline and your comments on mine.