Load management for generator-driven loads is common on large boats, and I used to make a box that did that. It was not sophisticated, just a pair of sockets wired so that if one was drawing current, the other was off. This is useful for turning off a water heater when the ac is running, so that the generator does not have to be sized for the combined load. We decided that there was little market for such a simple unit, so we only made 10 or so.
Today, the cost of inverters has come down so much that I am not sure there is any need for it. It is likely cheaper to just get an inverter that is large enough. 3kw matches the shorepower and a true sine-wave inverter for that can be had for around $400.
Interestingly, computer suppliers sell a similar thing that looks like a power strip, but with one "sensor" plug and a bunch of slave plugs. You can plug your monitor into the "sensor" plug, and all the other computer crap into the slaves. Then, when you turn your monitor on (or off) the whole magilla turns on (or off). I haven't tried one, because I have a laptop, but it might work onboard.....
1975 32' Flybridge Sedan, twin Perkins 6-354 diesels, 1:1.53 velvetdrives, 16 X 19 props. Merritt Island, Florida
