To be fair, Generations was something the "fan" designers at Hasbro have wanted to use to homage/redo as many of the early era characters as possible (the first 2-3 years)... throwing in the odd post-Gen1 character toy where possible (like Beasts), as well as having to commit their resources to fulfil any current event (like WFC, FOC, IDW, Movies).
Now that they have done a fair chunk of those first few years, later era Gen-1 figures start showing up on their "to do" list. Scoop is indeed an odd first choice for double-targetmasters... but as Lord Zed has speculated, it was probably chosen of the six as the easiest to redeco into another toy (to maximise sales). But I just don't think that they'd do Constructicons individually like that... as one-off figures, especially if there was no way of combining them.
They almost got away with doing it for Silverbolt and Onslaught because they were bigger, core figures of those teams... but the Constructicons were the first combiner for Transformers. Proving popular enough to spawn an enduring concept that has not only lasted 29 years (as they were in year 2), but is a concept that fans constantly demand of any new series, and is expected of anything that bears the Constructicons names. (like certain toys "should" be triplechangers if they bear a particular Gen1 name or attempt to homage them)