Sourdough starter experiment with probiotic capsule

Something tells me these bacteria like warm temperature around 37C. Are you keeping your starter warm?

Welcome aboard.

Nice experiment!    I'm a tinkerer too, and sometimes like to "play mad scientist."

My latest is "making" buttermilk by propagating the cultures from store-bought buttermilk with plain milk, then letting it sit at room temp overnight. Someone, I forget who, showed me this link:
http://benstarr.com/blog/all-about-buttermilk/
My "homemade buttermilk"  also increases in tanginess just sitting in the fridge. I've tinkered by adding some yogurt and cream cheese.

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Two of the real bread and microbiology experts here who I admire are:

https://www.thefreshloaf.com/user/mariana
and:
https://www.thefreshloaf.com/user/debra-wink

Hopefully, they will soon chime in.

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About yeast-vs-LAB, Mariana linked to a video, and wrote a good comment here:
https://www.thefreshloaf.com/comment/486405#comment-486405

Debra Wink's microbiology expertise is on display in these two posts:
https://www.thefreshloaf.com/node/10856/pineapple-juice-solution-part-1
https://www.thefreshloaf.com/node/10901/pineapple-juice-solution-part-2

Part 1 is super technical, Part 2 is more how-to about getting a starter going for the average home-kitchen baker.

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All I can offer is this: commercial Saccharomyces Cerevisiae is not a species of yeast that loves to live in symbiosis with the various acid producing bacteria. For that, you need one or more of the wild yeast species that are known to inhabit the surface of grains (such as wheat and rye) or fruit (such as grapes).

I think your system could work, but if it does, what may happen is this:  As the Saccharomyces Cerevisiae slowly dies off, it is also being replaced by feeding the ongoing starter with flour that is bringing in species of wild yeast that do love the LAB.

This is similar to what is recommended in the Poilane book: make a LAB/yeast starter out of yogurt, white flour, and WW flour, and commercial (Saccharomyces Cerevisiae) yeast.  But if the starter is maintained/fed long enough, the LAB and wild yeast brought in by the flour that is fed to it, eventually take over.

Dave makes a valid point about the yeasts. Seems logical with numerous feedings the wild yeasts that prefer an acidic environment would take over. And while I also love to experiment if this takes as long as the traditional way to make a starter then nothing has been gained. It's still very interesting though. 

I'm also under the impression that while the yeasts and bacteria in a sourdough/starter are varied and many it won't make a good home for every type of yeast and bacteria. So while you have thrown at it many lab grown bacteria it'll find an equilibrium. And on top of that you also find that one type of bacteria with accompanying yeast tends to be the more dominant ones at any one time. 

I just remembered another example of someone seeding a sourdough starter with one tiny individual granule of commercial bread yeast.

In the Laurel's Kitchen Bread Book, updated edition copyrighted 2003, pages 150 - 151, "Manuel's Rye Sour." 

She says the 1/2 tsp milk and literally one granule of yeast really made a difference, and that they tried it both with and without them.

Here's a similar approach you might find interesting:

https://www.thefreshloaf.com/node/59912/sour-dough-ferments-using-probiotics