Persnaly I don'tt think the Crystal staff thought the shitenou thing was mistake . I think the season's scripts were done a long time ago .So any references to it was never plan in begin with. ( Than again we probably won't know for certains unless we see the originals script)
I absolutely agree with you.
I don't think the writers regretted their choice to change DK: the changes were so important and I think they carefully thought of it and CHOSE it (I also think that Naoko Takeuchi was somehow involved in this change, giving her "OK").
The point is that, adapting the manga act after act the way they did left no place to any further development: so, the Sen/Shi thing was a bit "compressed", but overall the writers made a good job (they couldn't do much more with a 1:1 adaptation).
With BM and Infinity, of course, the writers focused on the plot, following the manga. It will happen also with Dream and Stars! To me, forgetting a major plot point of DK is a matter of laziness and poor writing: when it will come to Mars' dream in Dream, adapting it exactly as the manga wouldn't work 100% with the canon Mars/Jadeite THEY CREATED (it needs a slight change to keep the continuity along the arcs; I don't mean a PLOT continuity but a CHARACTER continuity: what Crystal lacked is the continuity about the Senshi's characters, to me, because of the changes made in DK and then forgotten).
It isn't a matter of "regretting" the changes but a matter of laziness and sometimes lacking in characters' deepness and continuity.
About the chance for the Senshi to fall in love with the Shitennou in the new timelife, well, it's the same of Mamoru and Usagi: kindred souls separated by a tragic destiny in their past life but reborn to meet again.
If the Shitennou were still alive, I don't find strange to have them falling in love with the Senshi all over again (like Usagi and Mamoru). I am pretty sure about it.
A little cameo of the Shitennou at Mamoru and Usagi's wedding would be fine, to me: perfect closing of a circle.
Ok. That's all. I won't talk any more about this topic.