Katarina was likely chosen because they did already work on a cyber skin for her once and wanted to finish said skin.
Ashe seems fine considering that a bow wielder with energy arrows seems a neat idea.
Ekko seems a bit odd,since like you say he is already pretty techy,but I guess his hologram following him simply fits the project series rather well.
In any case we should wait until we actually see the skins before we judge them.
As for the ones you mention:
Shen seems like a good choice,but maybe they didn't want a second ninja or have already a different skin for shen in the works.
J4 seems a bit odd.I know there is a fan concept of this skin that looks rather cool,but j4 has barely any particles and his ult doesn't fit the project theme(it is too physical,whereas project has lots of hologram spell effects)
Elise really seems odd,there isn't much that would speak for elise...