OK, I'll just go ahead and put on the Footkerchief hat (hey look, the hat puffs its pipe, too!), and say that putting in the search term "immigration" pulled up 5 obvious results on the first page (of six) for suggestions of limiting immigration wave sizes, and another half dozen that were talking about "immigration officers", which may well have the same role, but I didn't feel like actually being DILLIGENT and reading stuff or copy-pasting all those urls or anything.
Or in other words, yeah, this is common. Of course, it's also theoretically very easy to program in, if Toady wanted, compared to a very large number of other requests that are constantly raining down.
One thing I'd say, however, is that I would be opposed to a "cap", and would prefer a multiplier, instead. The way that immigration works now, the rate of immigrants is based upon a combination of wealth and how many dwarves die horrible, screaming deaths under your "care". If the population cap were given a simple straight-up arbitrary limit of, say, 5 per year or season, you would get 5 pretty much every time unless you were really screwing something up and getting tantrum spirals that scare off everyone.
I think it would be a much better way of handling things if generating enough wealth to start attracting a half dozen dwarves at a time was considered a goal, rather than a reason why non-legendaries are considered so cheap and easily replacable as to be executed by the dozen simply so that the player doesn't have to bother figuring out what to do with all the dwarves they have.