First of all, commercial arguments about Ume's works really lack in perspective. As an artist, Ume has already hit it huge with Madoka and Hidamari Sketch. There's absolutely no reason to expect her to make a work about incest or whatever just because "that's what Japan wants".
What it actually comes down to is what does Ume want. And in that regard, yes it's clear that Ume has a history of doing both yuri and het. (She also has a history of hardly ever edging past the line of subtext in her non-doujinshi works, this is in fact the more likely scenario for this series, you won't be seeing much het even if the story actually is heading in that direction.)
My own feelings about Ume are that, whatever her inclinations are regarding het, you will be extremely unlikely to ever see her actually shitting upon yuri. And that's what leads me to chapter 3. As an individual chapter, it has an effect of strongly reorienting the story towards yuri. For the story (interpreted as het/pseudo-incest romance) as a whole, it comes off as mildly schizophrenic. My personal interpretation is it's Ume backing off on the het/incest angle. A true yuri end would still be a surprise, but I don't expect the het now to get past subtext either.
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