I've finally gotten around to trying this strategy out using Mongolia on Immortal/Standard/Standard. I've restarted a few times after getting through the early game but then wishing I had done something differently so I've had a few runs of the opening but haven't gotten into late game yet. A few notes:
I am able to consistently get the desired pantheon (God of the Expanse) and have been able to found a religion almost every time with fairly minimal effort. A starting build of scout/monument/shrine and policy opening of Tradition->Sovereignty along with the Expanse pantheon seems to be enough to found a religion somewhat safely on Immortal difficulty. I typically don't prioritize shrines in my 2nd or 3rd cities as a monument or ger probably produces just as much faith via tile acquisition.
I have not been able to get Angkor Wat in any of my games, however. I have tried going to Writing and then to Commerce and every time I am still a few techs away from Commerce when Angkor Wat is completed. I am planning to do one more restart where I go straight to Commerce and can hopefully nab it this time.
Overall this opening can feel a tad slow in tech/policy progression but not much slower than normal IMO. I haven't been able to make it to mid or late game yet so it will be interesting to see what happens when all of the synergies come online and start snowballing. I'm planning to enhance with Zealotry to buy my armies with faith and also dip into Piety for the faith purchase cost reduction and double tile acquisition during WLTKD. I'll eventually go for Autocracy/Lebensraum for yet more tile acquisition and hopefully get Angkor Wat next time.
I'll conquer/puppet as much as I can and hopefully with enough cities popping new tiles the food/faith/gold instant incomes will just be massive. I'll try to report back when I've completed a game with my findings!
An update: I was able to get Angkor Wat in my new game. I only researched techs necessary for getting to Commerce in order to grab it. Even doing that, there were other civs grabbing wonders near that tech progression which makes me think I probably only barely got it. The trade off is that I didn't get to Writing until much later than normal so my tech progression has certainly suffered. It may prove to be worth it, though. We'll have to see how strong the border pop synergies are.
Despite being quite behind in tech I was still able to found 4 decent cities total and already forcefully annexed a nearby city state, so it seems like I should be in a good spot to recover in science and then see how the border blobs snowball works from there.