With an electronic regulator it's EASY to limit armature output current. Quite simply, you can do it by inserting some resistance in the field. I kind of tried to get that across in my last couple of posts.
So it would make a fairly simple project for someone with a little electrical savvy for example to adapt one of those cheap electronic JCWhitney alternator regulators, which don't have current limiting, to work on a genny. I did that with a spare Delco regulator I had.

One could design a regulator if he thought there was enough of a market. With the old bikes, there actually is a market for electronic regulators. But with trucks, it's so cheap to convert to an alternator and the benefit so great, it would seem there's little reason to spend money on an electronic voltage regulator for a generator, which wouldn't have the same bang for the buck.