Regarding suburban districts, this is really what the Democratic Party has to work with right now. The trends that have softened these districts up aren't new and have been developing for a long time now. I can understand why some don't like the idea of loading up the party full of politicians who serve such constituencies, knowing what it might entail, but trying to change course is something no one can control right now, and getting back certain types of districts the party has lost would take years, if it still is even possible.
Further, I might add, just because Democrats would come to more deeply represent suburbia does not necessarily mean its leftwards shift would suffer. People tend to support a wide range of policies as long as the party/politicians can adhere to certain principles.
Yeah, we have already seen this in polling data. College educated whites (people who live in the suburbs) are becoming more progressive.
It would be political malpractice to not try to win this voters over. Also flipping these voters would help Democrats in the future since they are the most likely to show up and vote in the mid-terms.