If I was in this situation here's what I'd probably do:

1.) Just make whatever YOU want, and people can pledge based on if they want to support YOU. That way, whatever money you get who cares, you're making the stories for yourself anyhow :P

OR (the second option isn't much different)

2.) Take away the requirement to write anything for patreon at all. Maybe some months you will, maybe other months you won't, again people are supporting YOU, not just throwing you money to get something. If they want to do that, then they can get a commission xD

Actually, looking at your patreon you haven't even met your goal where you said you'd write a story every month! Why are you bothering with it yet then? xD (Also up that goal price a bit if you want to make more per personal story) :3

If I were in your position, I'd be treating it as exactly that. A personal project.

You need to not worry too much about pleasing others with this. That's what the commissions are for, I'd wager that they're your main source of exposure and income. This is what you say it is. A side project, a way for you to build up your own world and your own characters interactions. This is as Mahiri thing, and so Mahiri rules supreme.

What you're saying would be incredibly difficult to do, and I'm not sure you could actually pull it off using the settings Patreon has. It's certainly not something I've ever seen, people only paying for certain submissions. I don't think that's workable or viable.

I understand you want to do this, and I think you should, I really do. I would love to hear about your world and characters and the stories that you can tell in that world, but you're getting hung up on the numbers, instead of treating this as what it should be, supplementary. Again, while I do not know your financials, I would assume Patreon isn't your primary source of income and even if you hit the goal you wanted to, it wouldn't be. From how you phrase it seems it would be the equivalent of just taking on another commission.

I think you should do what YOU want. Write the stories you want to see, with the pairings you want to see happen, and the stories you WANT to tell. Push your Patreon more, shout about it whenever you can, put a link at the bottom of every post, every journal and just keep at it. Aim for one post a month but if you can't hit that, then do every 2 months? Or as often as you can. I'm sure, eventually, you will hit the goals you want to, but that doesn't mean if it takes you a while to hit those goals that you should just give up on it. Hell, I'd argue this'd be good to do even without the Patreon as a break between commissions. Writing nothing but what other people want you to seems like a decent way to start burning yourself out.

My DMs on Telegram are open if you want to talk abut this a little more :3

What about a Vore patron and a non-vore patron? You would probably just want a $1 minimum in case someone wanted to subscribe to both, and a $2 alt minimum if someone only wanted to subscribe to one of the two. That might be more work, juggling both patrons, but one of them mill eventually dominate and tell you which is the more successful version. :)