Seeking publishing advice for an academic textbook
One factor you should keep in mind is that most academics consider publication to be permanent.  Books used to go out of print because it was economically infeasible to keep them available, but with print on demand and electronic publishing, there's a broad expectation that anything available now will remain available forever under similar terms.  This doesn't really apply to standardized low-level textbooks, which can disappear if unsuccessful and are regularly replaced with new editions if successful, but it applies to anything with noteworthy scholarly content.  Based on your stackexchange contributions, I bet your book will fall into this category (and I'm certainly looking forward to reading it).

In particular, if you publish a book through KDP and later withdraw it to do something else with the book, you may upset people.  I'd certainly be unhappy if I had decided to use the book in a course (or had recommended it widely to students) on the basis of price, only to discover that it had abruptly been removed from KDP and now cost substantially more from another publisher.

I assume you would have to remove it from KDP, and couldn't keep it there while publishing a paper edition elsewhere.  It doesn't seem impossible, but it's not plausible that another publisher would put work into promoting a book that was available much more cheaply online from a rival publisher.

I don't know how academic publishers would react to having had a previous edition published by KDP.  I'd bet they would be open to it in principle, the same way other books occasionally move between publishers when the rights are available, but I also suspect they'd worry about anchoring to a very low price.  I think the only way to know for sure is to ask representatives (for example, you can easily chat with them in person at big conferences), since reluctance to do this could easily vary between publishers.

I'd also keep two additional factors in mind:


Academics who are enthusiastic about electronic publishing are often wary of digital rights management.  By emphasizing this aspect, KDP may decrease some of the enthusiasm for this approach.
If your book is not particularly successful on KDP, it may undermine your negotiating position with mainstream publishers.  This means you may need a plan to get publicity for your book, since you won't have advertising (outside of the Amazon ecosystem) or bookstore sales.  There are a lot of factors that are difficult to predict.  For example, will anyone publish book reviews if the book appears to be essentially self published and you are said to be seeking a mainstream publisher?  If there are no reviews, it will hurt your visibility; if there are reviews, they probably won't review it again upon finding another publisher, which might lower other publishers' enthusiasm for taking it on.