Would it be hard to have an option like DP but without free great prophet, so you can found any religion you have the tech for but have to generate a great prophet normally. Those who want to have more religions just have to focus on GP and the tech leader don't have all religions without being limited to only founding one. Maybe also add an event that auto found an unfounded religions to avoid having civ that just can't get a great prophet (I don't think it will be a problem seeing as GP is one of the easiest great person to have especially early.)
I've been considering this extensively. Wondering if Divine Prophets should just remove the free prophet handouts and see what happens. Would definately make getting a religion a real challenge. I was also thinking it would benefit from having some early cheap buildings that create some GP pts or revamping the entire building line-up to have many add some GP pts even if not wonders. This would force players to specialize cities and take some major sacrifices to get the Great People they want so as to avoid corrupting the potential Great Person results or they'd end up with a total crapshoot. When religions (and eventual corporations) are on the line when GPs are born, that'd make for a more strategically difficult decision. You'd really have to go out of your way to make a prophet only birthing city (a religion center so to speak) but then it would also suffer from not having quite as many overall GP pts and would have a hard time keeping up with your more generic cities that build just about everything and total up a lot more GP pts that way. You'd probably then want to build the National Wonder in your religious center and get overall less GPs unless you're the gambling sort and go for massive amts of GP birthing in a highly populated 'build everything' style city. This style would likely not produce many Prophets. So yeah, I'm thinking this through but:
I have a few issues to work out first.
1) I'd make it an additional option that is nicely compatible with DP (No first-to-tech bonuses) The thinking extends to all first-to-tech benefits such as free technologies as well and overall would be a game for those who want to see more balance between the laggers and the leaders. I'm also debating making all wonders, national and otherwise, require a particular GP to build (since it will have so many more GPs being born overall and to give the non-prophets just as strong a cause to be born.) That's going to take a hell of a lot of planning and work and our building system keeps racing at a pace I can't currently keep up with so when that slows down I'll have more leeway here.
2) There are some AI considerations to make here. The AI needs to understand the option and play wisely in this environment (specializing their cities, moving the Divine Prophets they get to the right city for founding a religion (currently they just found where they are born which is conveniently in the capital if they got it from being first to the religious tech), some tweaks to how they utilize all other GPs to make sure they are building wonders in rational locations, etc...) Some of that stuff is still mysterious to my limited programming skills.
I mean... I could make a modified Divine Prophet option much as you suggest and just leave it as is. But for the ai, it would become a little too much of a random affair as to whether they ever get a religion (most of the prophets born are based on religious wonder buildings, many of which come from having religions chosen so it becomes conceivable they may never get a prophet without some ai tweaking... in otherwords, it would completely imbalance the usefulness of a prophet with the other forms of GPs and the ai would not be aggressive enough to understand this imbalance to their fullest advantage. It would take tweaking I'm not really prepared to do for such a minor project, if that makes any sense.) It would also be yet another incompatable option with Divine Prophets and Limited religions and I want to see an eventuality where DP and LR are fully compatible, bringing us back to a state where all options may be completely compatible when mixed and matched. (something I'll be working on here... possibly even this weekend.) I'd rather have an additional option that, when combined with DP, becomes much like the scenario you suggest, with some additional features to make all GP forms equally valuable even when balanced to the religion founding power of the Great Prophet.
So the next step down that road after creating complete compatibility between LR and DP would be to give us the No First-to-Tech benefits option that would trigger many buildings to be offering GP pts they currently do not but only when the option is on, and to disable the gifting of free techs, prophets, and other benefits for the first to reach a technology. This would make Prophets a touch imbalanced as they'd be the primary type you'd want to get.
Then add a Wonders require the Wonderful option that limits all wonders to being built by GPs, which would put all GPs in balance with one another. (I mean heck, many times an artist or an engineer would be a great result to help you get more prophets!)
I've been thinking about this mod plan for a while now and I just haven't moved forward much on it. It's quite an undertaking but could be very rewarding, providing very new ways to play with whole new dimensions of strategy in city design and nation management. It's perfect for C2C with all the added buildings and religions and such... would be really cool to implement, but its not going to be overnight at all.